[libclc] [libclc] Fix a couple of issues preventing in-tree builds (PR #87505)

[Michał Górny via cfe-commits]

mgorny wrote:

Thanks. This seems to fix that problem. However, now I'm seeing missing dep in build ordering:

```
[1793/1922] cd /tmp/portage/dev-libs/libclc-19.0.0.9999/work/libclc_build && /usr/lib/llvm/17/bin/llvm-spirv --spirv-max-version=1.1 -o spirv-mesa3d-.spv builtins.opt.spirv-mesa3d-.bc
FAILED: spirv-mesa3d-.spv /tmp/portage/dev-libs/libclc-19.0.0.9999/work/libclc_build/spirv-mesa3d-.spv 
cd /tmp/portage/dev-libs/libclc-19.0.0.9999/work/libclc_build && /usr/lib/llvm/17/bin/llvm-spirv --spirv-max-version=1.1 -o spirv-mesa3d-.spv builtins.opt.spirv-mesa3d-.bc
No such file or directory
[1794/1922] /usr/lib/llvm/17/bin/clang -DCLC_SPIRV64 -D__CLC_INTERNAL -I/usr/lib/llvm/17/include -I/tmp/portage/dev-libs/libclc-19.0.0.9999/work/libclc/generic/include -cl-no-stdinc -target spir64-- -fno-builtin -nostdlib -O0 -finline-hint-functions -I /tmp/portage/dev-libs/libclc-19.0.0.9999/work/libclc/generic/lib/shared -MD -MT CMakeFiles/builtins.link.spirv64-mesa3d-.dir/generic/lib/shared/vload.bc -MF CMakeFiles/builtins.link.spirv64-mesa3d-.dir/generic/lib/shared/vload.bc.d -o CMakeFiles/builtins.link.spirv64-mesa3d-.dir/generic/lib/shared/vload.bc -c /tmp/portage/dev-libs/libclc-19.0.0.9999/work/libclc/generic/lib/shared/vload.cl -emit-llvm
[1795/1922] cd /tmp/portage/dev-libs/libclc-19.0.0.9999/work/libclc_build && /usr/lib/llvm/17/bin/opt -o builtins.opt.spirv-mesa3d-.bc /tmp/portage/dev-libs/libclc-19.0.0.9999/work/libclc_build/builtins.link.spirv-mesa3d-.bc
```

Note that `builtins.link.spirv-mesa3d-.bc` is generated in step 1795, while it's used in 1793. Not sure if it's related, but I've never seen that one before.

https://github.com/llvm/llvm-project/pull/87505