Update uvwasi CMakeLists.txt

[kulcsaradam]

FetchContent_Populate is deprecated, updated the cmake file to use FetchContent_MakeAvailable.
Also updated minimum cmake version for FetchContent_MakeAvailable compatibility.
Also fix a bug where the flag '-m32' was not added when building in 32
bit mode.

[kulcsaradam]

The function FetchContent_Populate is being deprecated and should no longer be used according to Cmake. For reference: https://cmake.org/cmake/help/latest/policy/CMP0169.html#policy:CMP0169

It should be replaced by FetchContent_MakeAvailable, which was introduced in version 3.14, thus, if we replace FetchContent_Populate the miminum required cmake version should be updated too.

It is unclear when FetchContent_Populate or it's behavior will be removed or changed.

[clover2123]

Also fix a bug where the flag '-m32' was not added when building in 32 bit mode.

Is this right?
But 32 bit mode has been tested in our CI and it showed no errors.

[kulcsaradam]

On my stystem simply replacing the FetchContent function breaks the linking of uvwasi with walrus with a linker error:

/usr/bin/ld: _deps/libuv-build/CMakeFiles/uv.dir/src/fs-poll.c.o: file class ELFCLASS32 incompatible with ELFCLASS64
/usr/bin/ld: final link failed: file in wrong format

And also the most recent x86 CI run of the patch that got merged (commit 7800a31) into the main branch does not include -m32 as an option in it's cflags

- summary of build options:
    Install prefix:  /usr/local
    Target system:   Linux
    Compiler:
      C compiler:    /usr/bin/cc (GNU)
      CFLAGS:         

-- summary of uvwasi build options:

    Install prefix:  /usr/local
    Target system:   Linux
    Compiler:
      C compiler:    /usr/bin/cc
      CFLAGS:         

    LibUV libraries: uv_a
    LibUV includes:  /home/runner/work/walrus/walrus/out/linux/x86/_deps/libuv-src/include
    Debug logging:   
    Code coverage:   
    ASAN:            OFF
    Build tests:     OFF

-- Configuring done (3.1s)
-- Generating done (0.0s)
-- Build files have been written to: /home/runner/work/walrus/walrus/out/linux/x86

There are two possible fixes one of which I recently discovered:

1. Adding -m32 to CFLAGS or CXXFLAGS so it persists through the whole compilation.
2. Not changing add_compile_options but adding add_link_options( -m32 ) after it, so the option is present when linking.

I believe that the first method has more information, since the flag -m32 will be visible when running cmake, but I am open to either option.

[kulcsaradam]

Also an idea:
Should we add a CI that compiles 64 bit walrus on 32 bit system? I don't think that there are CIs for that, but please correct me if I am wrong.

[clover2123]

AFAIK CFLAGS is not explicitly set by add_compile_options.
The second approach, add_link_options( -m32 ) looks simple and better

[clover2123]

Should we add a CI that compiles 64 bit walrus on 32 bit system?

CI already compiles and tests 32bit mode in 64 bit environments.
I don't think its possible and necessary to build 64 bit in 32 bit systems.

[kulcsaradam]

AFAIK CFLAGS is not explicitly set by add_compile_options. The second approach, add_link_options( -m32 ) looks simple and better

In that case I will change the patch to use that option.

[clover2123]

LGTM