[libc++] Mark num_get.bench.cpp as unsupported in C++03

Author: philnik777

libcxx/test/benchmarks/locale/num_get.bench.cpp

@@ -7,6 +7,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+// UNSUPPORTED: c++03
+
 #include <ios>
 #include <locale>