WASM/WASI target

[guest271314]

What language does this apply to?
WebAssembly/WASI, and to some extent JavaScript.

Describe the problem you are trying to solve.

I'm trying to compile https://github.com/fails-components/webtransport to WASM using WASI-SDK.

Describe the solution you'd like

WASI-SDK toolchain doesn't have <sys/wait.h> which is referenced in compiler/subprocess.cc, so I'm getting this error

[ 32%] Building CXX object third_party/protobuf/CMakeFiles/libprotoc.dir/src/google/protobuf/compiler/subprocess.cc.obj
clang++: warning: -lwasi-emulated-signal: 'linker' input unused [-Wunused-command-line-argument]
/media/user/1/webtransport/transports/http3-quiche/third_party/protobuf/src/google/protobuf/compiler/subprocess.cc:43:10: fatal error: 'sys/wait.h' file not found
   43 | #include <sys/wait.h>
      |          ^~~~~~~~~~~~
1 error generated.
make[2]: *** [third_party/protobuf/CMakeFiles/libprotoc.dir/build.make:1213: third_party/protobuf/CMakeFiles/libprotoc.dir/src/google/protobuf/compiler/subprocess.cc.obj] Error 1
make[1]: *** [CMakeFiles/Makefile2:5416: third_party/protobuf/CMakeFiles/libprotoc.dir/all] Error 2
make: *** [Makefile:156: all] Error 2

Describe alternatives you've considered

I am not a CMake expert by any means. I changed the original CMakeList.txt to this, because from what I gather from the maintainer protobuf needs to be available on the native system, not compiled to WASM

IF(APPLE)
    set_target_properties(protoc libprotoc libprotobuf PROPERTIES OSX_ARCHITECTURES arm64;x86_64 CACHE STRING "Build architectures for Mac OS X" FORCE )
ELSEIF(CMAKE_SYSTEM_NAME STREQUAL "WASI")
    # Add any specific properties for WASI targets here if needed. 
    # The WASI toolchain usually handles the necessary flags automatically.
    # The original OSX_ARCHITECTURES property is irrelevant for WASI.
    execute_process(
        COMMAND uname -m
        OUTPUT_VARIABLE HOST_ARCH
        OUTPUT_STRIP_TRAILING_WHITESPACE
    )
    set_target_properties(protoc libprotoc libprotobuf
        PROPERTIES
            OSX_ARCHITECTURES "${HOST_ARCH}"
    )
ENDIF()

Next I tried just commenting out the whole subprocess.cc file, and that doesn't work, either.

Additional context
Add any other context or screenshots about the feature request here.

Issue where I try to get roadmap from maintainer, who is not interested in WASM support for their library fails-components/webtransport#354.