spirv: OpenCL printf support

[ivanstepanovftw]

I want to have std.debug.printf() implemented for GPGPU, because it lowers entry point for newcomers, and this feature allows to catch bugs faster (like I had with signed_integer - 0).

To test this PR you need to clone zig-spirv-test-executor in root dir and run:

./build/stage3/bin/zig build -p stage4 -Denable-llvm -Dno-lib
./stage4/bin/zig build --build-file ./zig-spirv-test-executor/build.zig
export RUSTICL_ENABLE=llvmpipe
./stage4/bin/zig test ./test/behavior/asm.zig \
    --test-runner ./zig-spirv-test-executor/src/test_runner.zig \
    -target spirv64-opencl-none \
    -mcpu generic+int64+float64+float16 \
    -fno-llvm \
    --test-cmd ./zig-spirv-test-executor/zig-out/bin/zig-spirv-test-executor \
    --test-cmd --platform \
    --test-cmd rusticl \
    --test-cmd-bin

Better to review per commit.

[alichraghi]

I suggest you to not integrate it with std.debug.print and instead have std.gpu.printf which doesn't try to integrate with any zig formatting and is just a simple call to OpenCL's printf.

[ivanstepanovftw]

This is unrelated change to the PR - I hoped to make better "string constants with c constraint" testing in tests/behavior/asm.zig. It does work though.

[ivanstepanovftw]

Should I drop this commit since I am not trusted and no single test cover this?

[alichraghi]

Nah it looks correct

[alichraghi]

I have a few nitpicks that i can fix myself but otherwise LGTM. Hopefully we can switch to an std.format version later

[ivanstepanovftw]

Rebased.

[ivanstepanovftw]

Cannot test with recent changes.

Tracking:

• (!) comprimePrintf broken spirv comptime comptimePrint broken #24538
• (!) refactoring regression spirv codegen Invalid extended instruction import 'open_cl_std' #24539
• Update to Zig 0.15.0-dev.1160+e43617e68 Snektron/zig-spirv-test-executor#4
• Update to Zig 0.15.0-dev.1160+e43617e68 Snektron/opencl-zig#4 (test runner deps)