Use Clang's __has_* macros in Compiler.h to test for features
When targetting Windows, clang does not define __GNUC__, and as a result
we don't use our attributes with it. This leads to warnings about
unused functions that are already annotated with LLVM_ATTRIBUTE_UNUSED.
Rather than testing for __clang__, we can use its __has_attribute and
__has_builtin macros directlty.
While I'm here, conditionally define and use __GNUC_PREREQ for gcc
version checks. Spelling the check out with three comparisons is
verbose and error prone.
Reviewers: aaron.ballman
Differential Revision: http://llvm-reviews.chandlerc.com/D1080
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185831
91177308-0d34-0410-b5e6-
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