Add new C++ headers <cerrno> and <cfloat>

Also add std::malloc/realloc/calloc/free to <cstdlib>
Rename <cwchar_is_not_supported> to <cwchar>
diff --git a/libstdc++/include/cstdlib b/libstdc++/include/cstdlib
index 9e8a7ce..5e6a0b3 100644
--- a/libstdc++/include/cstdlib
+++ b/libstdc++/include/cstdlib
@@ -85,6 +85,11 @@
 using ::random;
 using ::srandom;
 
+using ::malloc;
+using ::free;
+using ::calloc;
+using ::realloc;
+
 using ::unlockpt;
 using ::ptsname;
 using ::ptsname_r;