project-specific headers should use "". Keep #include <amdhsa_abi.h>
llvm-diff shows no change to libclc.bc for spir--, spir64--, nvptx64--,
nvptx64--nvidiacl, nvptx64-nvidia-cuda and amdgcn-amd-amdhsa-llvm when
LIBCLC_TARGETS_TO_BUILD is "all".
Verified that reversing spir64--/libclc.spv and spir--/libclc.spv to
LLVM bitcode shows no diff.
Also fix `__CLC_INTEGER_CLC_BITFIELD_EXTRACT_SIGNED_H__` guard per
copilot review.
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Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>