Instead of checking _LIBCPP_LOCALE_L_EXTENSIONS all over, instead check it
once, and define the various *_l symbols once. The private redirector symbol
names are all prefixed with _libcpp_* so that they won't conflict with user
symbols, and so they won't conflict with future C library symbols. In
particular, glibc likes providing private symbols such as __locale_t, so we
should follow a different naming pattern (like _libcpp_*) to avoid problems
on that front.
Tested on Linux with glibc. Hoping for the best on OSX and the various BSDs.
http://reviews.llvm.org/D17456
git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@263016 91177308-0d34-0410-b5e6-96231b3b80d8
