[libc++] Add missing locale aliases

Add underscore aliases for strtof_l and strtod_l. _strtold_l exists in
VS 2013 and above, so fix that definition as a drive-by fix.

Differential Revision: https://reviews.llvm.org/D25059

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@282681 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed