This prevents the weird failures I saw on macOS in #17856; instead, it
should fail on *all* platforms with
Unhandled exception ("epan/proto.c:8800: failed assertion "DISSECTOR_ASSERT_NOT_REACHED"", group=1, code=6)
(which it does on macOS 11.6/Xcode 12.5.1 and Windows 10/VS 2019
16.11.8; according to
https://en.wikipedia.org/w/index.php?title=Thread-local_storage&oldid=1064900318#C_and_C++
the major UN*X C compilers support __thread and the major Windows C
compilers support __declspec(thread).).
@jvalverde: on branches that require C11/C++11 support, we could perhaps
just use _Thread_local for C and thread_local for C++. Note that
<thread.h> is optional in C11, and macOS 11.6/Xcode 12.5.1 does not
appear to include it.)
This does not *fix* the aforementioned issue; to do *that* we need to do
TRY in the register-dissectors thread code. I'm committing this
separately because it fixes a bug in our exception package that could
cause all sorts of randomness now and in the future - what we're doing
now is Just Wrong.
(Yes, there's code to support per-thread exception handler stacks *on
platforms with pthreads*, but this is simpler *and* also works on
Windows.)
db27fb777a