make sure getw/putw agree with prototypes by defining _GNU_SOURCE

src/stdio/getw.c

@@ -1,3 +1,4 @@
+#define _GNU_SOURCE
 #include <stdio.h>
 
 int getw(FILE *f)

src/stdio/putw.c

@@ -1,3 +1,4 @@
+#define _GNU_SOURCE
 #include <stdio.h>
 
 int putw(int x, FILE *f)