Update fuchsia.h

Use clocale so std::localeconv works.

Author: mysterymath

libcxx/include/__locale_dir/support/fuchsia.h

@@ -12,7 +12,7 @@
 #include <__config>
 #include <cstdlib>
 #include <cwchar>
-#include <locale.h> // uselocale & friends
+#include <clocale> // uselocale & friends
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header