Allow building libc++ with any custom -std=xxx flag.  Note that using -std=gnu++98 will give a lot of warnings with clang, so please use -std=c++0x or higher, or use NO_WERROR.
Allow building libc++ with any custom -std=xxx flag.  Note that using
-std=gnu++98 will give a lot of warnings with clang, so please use
-std=c++0x or higher, or use NO_WERROR.

MFC after:	1 week

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase