bsd-user/mmap.c: Move __thread attribute to right place

Avoid a compiler warning on OpenBSD:
bsd-user/mmap.c:28:1: warning: '__thread' is not at beginning of declaration [-Wold-style-declaration]
by moving the __thread attribute to its proper place.
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Reviewed-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 1500395194-21455-2-git-send-email-peter.maydell@linaro.org

bsd-user/mmap.c

@@ -25,7 +25,7 @@
 //#define DEBUG_MMAP
 
 static pthread_mutex_t mmap_mutex = PTHREAD_MUTEX_INITIALIZER;
-static int __thread mmap_lock_count;
+static __thread int mmap_lock_count;
 
 void mmap_lock(void)
 {