Compilation failure due to: SPIRV-Tools removed WebGPU support

[timvpGoogle]

SPIRV-Tools removed WebGPU support:
KhronosGroup/SPIRV-Tools#4108

So shaderc no longer compiles due to missing symbols:

    [1344/22848] CXX obj/third_party/shaderc/src/shaderc_util_sources/spirv_tools_wrapper.obj
    FAILED: obj/third_party/shaderc/src/shaderc_util_sources/spirv_tools_wrapper.obj
    C:\b\s\w\ir\cache\goma\client\gomacc.exe ..\..\third_party\llvm-build\Release+Asserts\bin\clang-cl.e...(too long)
    ../../third_party/shaderc/src/libshaderc_util/src/spirv_tools_wrapper.cc(149,19): error: no member named 'RegisterVulkanToWebGPUPasses' in 'spvtools::Optimizer'
    optimizer.RegisterVulkanToWebGPUPasses();