[CMake] Use -std=c++11 if supported
[CMake] Use -std=c++11 if supported

Summary: This patch adds a check for if -std=c++11 is a supported flag, and adds it to CMAKE_CXX_FLAGS if it is supported.

Reviewers: EricWF

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D24007

git-svn-id: 6a9f6578bdee8d959f0ed58970538b4ab6004734@280021 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/libcxxabi,llvm-mirror/libcxxabi,llvm-mirror/libcxxabi,llvm-mirror/libcxxabi,llvm-mirror/libcxxabi