set(OQS_USE_PTHREADS OFF) on MinGW/Cygwin

[zxjtan]

Fixes #1693.
Looks like if cross-compiling from POSIX to Windows, the CMake detect pthreads as available on the host and sets OQS_USE_PTHREADS ON for compilation, which will not work on windows.

[baentsch]

Thanks for the quick fix, @zxjtan ! Would it be OK for you to try adding a cross-build job to CI so this doesn't occur again, e.g., here? Edit/Add: No problem if that's not so straightforward for you; will do a separate PR otherwise.

[zxjtan]

Thanks for the quick fix, @zxjtan ! Would it be OK for you to try adding a cross-build job to CI so this doesn't occur again, e.g., here? Edit/Add: No problem if that's not so straightforward for you; will do a separate PR otherwise.

Looks easy enough if there is a container that installs gcc-mingw-w64, but there does not seem to be one.

[SWilson4]

This seems to fix the pthread linking issue, but in turn another issue appears (at least for me, running in our Focal Docker container). Running

cmake -GNinja -DCMAKE_TOOLCHAIN_FILE=../.CMake/toolchain_windows-amd64.cmake -DOQS_DIST_BUILD=ON -DBUILD_SHARED_LIBS=ON .. && ninja

leads to further linking errors, this time seemingly to do with our internal API :(

However, this change does make the build pass with -DOQS_BUILD_ONLY_LIB=ON set, so it certainly moves the ball down the field. I suggest that we merge this as-is. I can investigate the internal API linking issue (they're probably due to my work) and add the CI test in the PR to address that issue. How does that sound @baentsch @zxjtan ?

[zxjtan]

@SWilson4 If the Focal container is ci-ubuntu-focal-x86_64, gcc-mingw-w64 is not in the install command. Could that be the cause of a problem?

[baentsch]

As per discussion. Adding cross-build CI in a separate PR.

[SWilson4]

@SWilson4 If the Focal container is ci-ubuntu-focal-x86_64, gcc-mingw-w64 is not in the install command. Could that be the cause of a problem?

I don't think so; I'm using a container based on that one on my local machine, and I installed gcc-mingw-w64 via apt.