bsd-user: Suppress gcc 4.x -Wpointer-sign (included in -Wall) warning

This is the same change as b55266b5 in linux-user.
Signed-off-by: NEd Maste <emaste@freebsd.org>
Message-id: 1459867593-72017-1-git-send-email-emaste@freebsd.org
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

bsd-user/uaccess.c

@@ -51,7 +51,7 @@ abi_long target_strlen(abi_ulong guest_addr1)
         ptr = lock_user(VERIFY_READ, guest_addr, max_len, 1);
         if (!ptr)
             return -TARGET_EFAULT;
-        len = qemu_strnlen((char *)ptr, max_len);
+        len = qemu_strnlen((const char *)ptr, max_len);
         unlock_user(ptr, guest_addr, 0);
         guest_addr += len;
         /* we don't allow wrapping or integer overflow */