Convert the Solaris xlocale.c compatibility library from plain C to C++ in order to fix the build failures caused by the addition of -std=c++11 to LIBCXX_COMPILE_FLAGS. The additional flag got propagated to the C file, resulting in error with strict compilers. Differential Revision: https://reviews.llvm.org/D25431 git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@284494 91177308-0d34-0410-b5e6-96231b3b80d8