Windows clang build fails with -Werror,-Wcast-function-type-mismatch

[vszakats]

Problem:

When building AWS-LC for Windows using clang and mingw-w64, the build fails with:

/path/to/awslc/crypto/rand_extra/windows.c:68:22: error: cast from 'FARPROC' (aka 'long long (*)()')
to 'ProcessPrngFunction' (aka 'int (*)(unsigned char *, unsigned long long)') converts
to incompatible function type [-Werror,-Wcast-function-type-mismatch]
   68 |   g_processprng_fn = (ProcessPrngFunction)GetProcAddress(hmod, "ProcessPrng");
      |                      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 error generated.

Full log: https://github.com/curl/curl-for-win/actions/runs/11712448493/job/32623148501#step:3:3996

Relevant details

AWS-LC commit: 1.37.0

System information: for linux, below info can be collected by running uname -srvmp

• CPU architecture: x86_64
• OS: Windows (cross-built from Debian testing)

Build log:

-- The C compiler identification is Clang 19.1.2
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /usr/bin/clang-19 - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- The CXX compiler identification is Clang 19.1.2
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/clang++-19 - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Go not found. Disabling some code generation and using pre-generated code in generated-src/
-- Perl not found. Disabling some code generation and using pre-generated code in generated-src/
-- Setting CMAKE_C_STANDARD=11
-- stdalign_check.c probe is positive, enabling AWS_LC_STDALIGN_AVAILABLE
-- builtin_swap_check.c probe is positive, enabling AWS_LC_BUILTIN_SWAP_SUPPORTED
-- The ASM_NASM compiler identification is NASM
-- Found assembler: /usr/bin/nasm
Copying platform assembly files from /home/runner/work/curl-for-win/curl-for-win/awslc/generated-src/win-x86_64/crypto/ to /home/runner/work/curl-for-win/curl-for-win/awslc/_x64-win-ucrt-bld/crypto
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD - Success
-- Found Threads: TRUE
-- Configuring done (1.1s)
-- Generating done (0.1s)