[clang] Set CMP0075 to new
[clang] Set CMP0075 to new

Make the check_include_file* macros honor CMAKE_REQUIRED_LIBRARIES. This
shouldn't cause any of the configuration checks to give different
results, and I verified that a clean configure before and after this
change resulted in identical CMake caches on my machine. The same change
was done for LLVM in r346377.

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@346378 91177308-0d34-0410-b5e6-96231b3b80d8

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