Built TclTLS 1.7.21 on MacOS 10.6, against Tcl 8.6.10 and OpenSSL 1.1.1g.
Building went okay (once I figured out I need to make sure gen_dh_params
finds up the right version of the openssl program), and make test works.

Then I try the following minimal https operation:

% package require tls
1.7.21
% package require http
2.9.1
% http::register https 443 [list ::tls::socket -autoservername true -require true -cafile
443 {::tls::socket -autoservername true -require true -cafile
% set tok [http::geturl

Under tclsh, that works fine.
Under wish, it segfaults! Consistently.

More detailed breakdown, with debug build of tcltls:

----------- Begin output:
% package require tls
./tls.c:1779:Tls_Init():Called
./tls.c:1897:TlsLibInit():Called
./tlsBIO.c:53:BIO_new_tcl():BIO_new_tcl() called
./tlsBIO.c:66:BIO_new_tcl():Asked to setup a NULL state, just creating the initial configuration
1.7.21
% package require http
2.9.1
% http::register https 443 [list ::tls::socket -autoservername true -require true -cafile
443 {::tls::socket -autoservername true -require true -cafile
% set tok [http::geturl
./tls.c:759:ImportObjCmd():Called
./tls.c:1093:CTX_Init():Called
line 2: 67253 Segmentation fault      "$(dirname "$@"
----------- End output.

----------- Begin crash report:
Process:         Wish [67253]
Path:
Identifier:      com.tcltk.wish
Version:         8.6.10 (8.6.10)
Code Type:       X86-64 (Native)
Parent Process:  sh [67251]

Date/Time:       2020-08-19 11:21:01.998 +0200
OS Version:      Mac OS X 10.6.8 (10K549)
Report Version:  6

Interval Since Last Report:          84517688 sec
Crashes Since Last Report:           808
Per-App Interval Since Last Report:  62722 sec
Per-App Crashes Since Last Report:   5
Anonymous UUID:                      1739C455-2439-487D-9ED0-2084ED6CAF3F

Exception Type:  EXC_BAD_ACCESS (SIGSEGV)
Exception Codes: KERN_INVALID_ADDRESS at 0x0000000000000000
Crashed Thread:  0  Dispatch queue: com.apple.main-thread

Thread 0 Crashed:  Dispatch queue: com.apple.main-thread
0   libSystem.B.dylib             	0x00007fff870ed7ee pthread_rwlock_wrlock + 50
1   libcrypto.1.1.dylib           	0x00000001150661ec CRYPTO_atomic_add + 44
2   libcrypto.1.1.dylib           	0x0000000114f77041 DH_up_ref + 33
3   libcrypto.1.1.dylib           	0x0000000114fff028 EVP_PKEY_set1_DH + 104
4   libssl.1.1.dylib              	0x0000000114d454f2 ssl3_ctx_ctrl + 1538
5   tcltls.dylib                  	0x00000001006351c3 ImportObjCmd + 2963 (.tls.c:1265)
6   Tcl                           	0x000000010018496f Tcl_ListMathFuncs + 3856
7   Tcl                           	0x000000010017e279 TclNRRunCallbacks + 58
8   Tcl                           	0x0000000100202fa3 Tcl_RecordAndEvalObj + 499
9   Tcl                           	0x0000000100203003 Tcl_RecordAndEval + 70
10  Tk                            	0x000000010002c91a TkPointerEvent + 19546
11  Tcl                           	0x000000010020d98c Tcl_NotifyChannel + 219
12  Tcl                           	0x0000000100272f3d Tcl_Sleep + 923
13  Tcl                           	0x0000000100226605 Tcl_ServiceEvent + 147
14  Tcl                           	0x00000001002268f5 Tcl_DoOneEvent + 314
15  Tk                            	0x000000010001ee29 Tk_MainLoop + 24
16  Tk                            	0x000000010002d24a Tk_MainEx + 2067
17  Wish                          	0x0000000100005141 0x100000000 + 20801
18  Wish                          	0x000000010000507c 0x100000000 + 20604

Thread 1:  Dispatch queue: com.apple.libdispatch-manager
0   libSystem.B.dylib             	0x00007fff870a5c0a kevent + 10
1   libSystem.B.dylib             	0x00007fff870a7add _dispatch_mgr_invoke + 154
2   libSystem.B.dylib             	0x00007fff870a77b4 _dispatch_queue_invoke + 185
3   libSystem.B.dylib             	0x00007fff870a72de _dispatch_worker_thread2 + 252
4   libSystem.B.dylib             	0x00007fff870a6c08 _pthread_wqthread + 353
5   libSystem.B.dylib             	0x00007fff870a6aa5 start_wqthread + 13

Thread 2:
0   libSystem.B.dylib             	0x00007fff870d0932 select$DARWIN_EXTSN + 10
1   Tcl                           	0x0000000100273f38 Tcl_InitNotifier + 1582
2   libSystem.B.dylib             	0x00007fff870c5fd6 _pthread_start + 331
3   libSystem.B.dylib             	0x00007fff870c5e89 thread_start + 13

Thread 0 crashed with X86 Thread State (64-bit):
  rax: 0x0000000000000000  rbx: 0x0000000000000000  rcx: 0x0000000000000000  rdx: 0x00007fff5fbfc5fc
  rdi: 0x0000000000000000  rsi: 0x0000000000000001  rbp: 0x00007fff5fbfc5b0  rsp: 0x00007fff5fbfc570
   r8: 0x0000000114f14aa0   r9: 0x00000001004fc0a4  r10: 0x0000000000000015  r11: 0x0000000100495c80
  r12: 0x00000001004977a8  r13: 0x0000000000000001  r14: 0x00007fff70c83cc0  r15: 0x0000000100878a10
  rip: 0x00007fff870ed7ee  rfl: 0x0000000000010246  cr2: 0x0000000000000000

Binary Images:
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    0x7fff8a111000 -     0x7fff8a13cff7  libxslt.1.dylib 3.24.0 (compatibility 3.0.0) <3630A97F-55C1-3F34-CA63-3847653C9645>
    0x7fff8a13d000 -     0x7fff8a160fff  com.apple.opencl 12.3.6 (12.3.6) <42FA5783-EB80-1168-4015-B8C68F55842F>
    0x7fff8a17d000 -     0x7fff8a182fff  libGIF.dylib ??? (???) <3BAD0DE8-8151-68B0-2244-A4541C738972>
    0x7fff8a183000 -     0x7fff8a199fef  libbsm.0.dylib ??? (???) <0321D32C-9FE1-3919-E03E-2530A0C1191B>
    0x7fff8a1f9000 -     0x7fff8a1fcff7  libCoreVMClient.dylib ??? (???) <75819794-3B7A-8944-D004-7EA6DD7CE836>
    0x7fff8a1fd000 -     0x7fff8a237fff  libcups.2.dylib 2.8.0 (compatibility 2.0.0) <4F2A4397-89BD-DEAC-4971-EE838FFA0964>
    0x7fff8a238000 -     0x7fff8a24afe7  libsasl2.2.dylib 3.15.0 (compatibility 3.0.0) <30FE378B-99FE-8C7C-06D0-A3AA0A0A70D4>
    0x7fff8a267000 -     0x7fff8a269fff  com.apple.print.framework.Print 6.1 (237.1) <CA8564FB-B366-7413-B12E-9892DA3C6157>
    0x7fff8a4b1000 -     0x7fff8a5d0ff7  libcrypto.0.9.8.dylib 0.9.8 (compatibility 0.9.8) <0CE8D59B-D0C7-1DCE-3654-37F27F61BEFA>
    0x7fff8a67b000 -     0x7fff8a7b9fff  com.apple.CoreData 102.1 (251) <9DFE798D-AA52-6A9A-924A-DA73CB94D81A>
    0x7fff8a7ba000 -     0x7fff8a7cbff7  libz.1.dylib 1.2.3 (compatibility 1.0.0) <97019C74-161A-3488-41EC-A6CA8738418C>
    0x7fff8a7d5000 -     0x7fff8a7d8ff7  com.apple.securityhi 4.0 (36638) <AEF55AF1-54D3-DB8D-27A7-E16192E0045A>
    0x7fff8a7d9000 -     0x7fff8a7d9ff7  com.apple.Cocoa 6.6 (???) <C69E895A-1C66-3DA9-5F63-8BE85DB9C4E1>
    0x7fffffe00000 -     0x7fffffe01fff  libSystem.B.dylib ??? (???) <9AB4F1D1-89DC-0E8A-DC8E-A4FE4D69DB69>

Model: MacBookPro7,1, BootROM MBP71.0039.B0B, 2 processors, Intel Core 2 Duo, 2.4 GHz, 4 GB, SMC 1.62f7
Graphics: NVIDIA GeForce 320M, NVIDIA GeForce 320M, PCI, 256 MB
Memory Module: global_name
AirPort: spairport_wireless_card_type_airport_extreme (0x14E4, 0x8D), Broadcom BCM43xx 1.0
Bluetooth: Version 2.4.5f3, 2 service, 12 devices, 1 incoming serial ports
Network Service: AirPort, AirPort, en1
Serial ATA Device: HL-DT-ST DVDRW  GS23N
USB Device: Built-in iSight, 0x05ac  (Apple Inc.), 0x8507, 0x24600000 / 2
USB Device: USB to ATA/ATAPI Bridge, 0x357d, 0x7788, 0x26400000 / 3
USB Device: Internal Memory Card Reader, 0x05ac  (Apple Inc.), 0x8403, 0x26100000 / 2
USB Device: BRCM2046 Hub, 0x0a5c  (Broadcom Corp.), 0x4500, 0x06600000 / 4
USB Device: Bluetooth USB Host Controller, 0x05ac  (Apple Inc.), 0x8213, 0x06610000 / 5
USB Device: IR Receiver, 0x05ac  (Apple Inc.), 0x8242, 0x06500000 / 3
USB Device: Apple Internal Keyboard / Trackpad, 0x05ac  (Apple Inc.), 0x0237, 0x06300000 / 2
----------- End crash report.

As far as I can tell, what is going on here is that OpenSSL wants to
increase the refcount on those darn DH params (or maybe part thereof),
seeks to acquire a lock on that refcount, and then crashes.

It's worth noticing contains
a number of implementations of the CRYPTO_UP_REF and CRYPTO_DOWN_REF
operations, most of which don't seem to use the final lock parameter
of these macros, but my compiler ends up using the very last definition,
which calls various pthread_??? functions with that as argument, so
someone forgetting to initialise that lock could handily explain what
is going wrong here.
Whether that error would be on the part of OpenSSL or TclTLS, however,
I couldn't say. But all OpenSSL tests pass.