Disabling signals is broken in V3

[petermost]

Describe the bug
It is not possible to disable signals in Catch2 V3 when it is prebuild into a static library.

Expected behavior
In V2 it was possible to disable signals/SEH with defining CATCH_CONFIG_NO_POSIX_SIGNALS and CATCH_CONFIG_NO_WINDOWS_SEH because it was a header only library. It would be nice if this would also possible for V3 without the need to build the library yourself.

Reproduction steps
The problem is also described here:
#1295 (comment)
The example code is trying to disable the signals like in V2, but in V3 these defines need to be defined when building the library itself.

Platform information:

• OS: Linux / Windows
• Catch version: v3

Additional context
I'm maintaining a fork of Sourcetrail which contains tests for JNI/JVM function calls. The JVM is internally using signals and this will lead to test failures because Catch2 intercepts these signals and reports a SIGSEGV.

I probably don't need to mention this, but this issue might become more urgent when Debian/Ubuntu starts to deploy a prebuild Catch2 V3 via their repositories.

[AlexisWilke]

I concur. The current implementation uses the same compile time flag (CATCH_CONFIG_NO_POSIX_SIGNALS) but since we now have a compiled version of the library, trying to change that flag in each individual project is futile.

On my end, I'll look to having two versions available for my projects. I have a couple of libraries where I want to be able to test Unix signals and as it stands, Catch2 v3 prevents me from doing it. It's a rather rare situation, but certainly useful to properly document if it is not going to be possible to switch the library one way or the other when used in different projects.