[libcxx] Fix build breakage on mips

Fixes https://bugs.llvm.org/show_bug.cgi?id=43011 caused by
https://reviews.llvm.org/D63284.

Committing as obvious.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@369364 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed