[libclc] [libclc][NFC] Prioritize clang's built-in opencl-c-base.h over CPATH versions (PR #177754)

[Joseph Huber via cfe-commits]

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@@ -411,7 +420,7 @@ foreach( t ${LIBCLC_TARGETS_TO_BUILD} )
       -I${CMAKE_CURRENT_SOURCE_DIR}/clc/include
       # Error on undefined macros
       -Werror=undef
-      -fdiscard-value-names
+      -fdiscard-value-names -nostdinc
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jhuber6 wrote:

Usually `-nostdlibinc` is the go-to for removing every implicit path except for the resource directory.

https://github.com/llvm/llvm-project/pull/177754