FreeBSD/src a600a25 (r354625)contrib/libc++/include cmath

Merge commit 371ea70bb from llvm git (by Louis Dionne):

  [libc++] Harden usage of static_assert against C++03

  In C++03, we emulate static_assert with a macro, and we must
  parenthesize multiple arguments.

  llvm-svn: 373328

This is a follow-up to r354460, which causes errors for pre-C++11
programs using <cmath>, similar to:

/usr/include/c++/v1/cmath:622:68: error: too many arguments provided to
function-like macro invocation

Reported by:    antoine
MFC after:      immediately (because of ports breakage)
DeltaFile
+2-2contrib/libc++/include/cmath
+2-21 files

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