fix invalid free of duplocale object when malloc has been replaced

newlocale and freelocale use __libc_malloc and __libc_free, but
duplocale used malloc. If malloc was replaced, this resulted in
invalid free using the wrong allocator when passing the result of
duplocale to freelocale.

Instead, use libc-internal malloc for duplocale.

This bug was introduced by commit
1e4204d522.

src/locale/duplocale.c

@@ -3,6 +3,11 @@
 #include "locale_impl.h"
 #include "libc.h"
 
+#define malloc __libc_malloc
+#define calloc undef
+#define realloc undef
+#define free undef
+
 locale_t __duplocale(locale_t old)
 {
 	locale_t new = malloc(sizeof *new);