Fixes for clang

Author: 32bitmicro

projects/hello_world/serial/hello_serial.c

@@ -9,7 +9,9 @@
 #include "pico/stdlib.h"
 
 /* For pritnf */
+#ifdef __clang__
 FILE *const stdout = NULL;
+#endif
 
 int main() {
     stdio_init_all();

projects/hello_world/usb/hello_usb.c

@@ -8,8 +8,10 @@
 #include <stdio.h>
 #include "pico/stdlib.h"
 
-/* For pritnf */
+/* For pritnf and clang */
+#ifdef __clang__
 FILE *const stdout = NULL;
+#endif
 
 int main() {
     stdio_init_all();