Initialize codecvt explicitly with the C locale, which might not be 0.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@181534 91177308-0d34-0410-b5e6-96231b3b80d8

src/locale.cpp

@@ -1376,7 +1376,7 @@ locale::id codecvt<wchar_t, char, mbstate_t>::id;
 
 codecvt<wchar_t, char, mbstate_t>::codecvt(size_t refs)
     : locale::facet(refs),
-      __l(0)
+      __l(_LIBCPP_GET_C_LOCALE)
 {
 }