Fix Sparse warning about missing prototype

Signed-off-by: Blue Swirl <blauwirbel@gmail.com>

bsd-user/elfload.c

@@ -545,8 +545,6 @@ static inline void memcpy_fromfs(void * to, const void * from, unsigned long n)
         memcpy(to, from, n);
 }
 
-extern unsigned long x86_stack_size;
-
 static int load_aout_interp(void * exptr, int interp_fd);
 
 #ifdef BSWAP_NEEDED

bsd-user/qemu.h

@@ -193,6 +193,9 @@ void mmap_fork_start(void);
 void mmap_fork_end(int child);
 #endif
 
+/* main.c */
+extern unsigned long x86_stack_size;
+
 /* user access */
 
 #define VERIFY_READ 0