libc: silence missing prototype warning

Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>

libc/stdlib/system.c

@@ -18,6 +18,7 @@
 #include <sysdep-cancel.h>
 #endif
 
+extern __typeof(system) __libc_system;
 #if !defined __UCLIBC_HAS_THREADS_NATIVE__
 /* uClinux-2.0 has vfork, but Linux 2.0 doesn't */
 #include <sys/syscall.h>
@@ -25,7 +26,6 @@
 # define vfork fork
 #endif
 
-extern __typeof(system) __libc_system;
 int __libc_system(const char *command)
 {
 	int wait_val, pid;