Allow copy elision in path concatenation
Allow copy elision in path concatenation

Summary:
Just port of libstdc++'s fix to libc++ fs: https://github.com/gcc-mirror/gcc/commit/e6ac4004fe49d785c63bf87aec4b095b5ce1d19f

Author of fix: Jonathan Wakely

Reviewers: EricWF, mclow.lists

Reviewed By: EricWF

Subscribers: smeenai, christof, cfe-commits, llvm-commits

Differential Revision: https://reviews.llvm.org/D46593

git-svn-id: 756ef344af921d95d562d9e9f9389127a89a6314@331910 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx