bsd-user: Move system call building to os-syscall.c

Signed-off-by: Warner Losh <imp@bsdimp.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

bsd-user/freebsd/meson.build

@@ -1,3 +1,4 @@
 bsd_user_ss.add(files(
   'os-sys.c',
+  'os-syscall.c',
 ))

bsd-user/meson.build

@@ -13,7 +13,6 @@ bsd_user_ss.add(files(
   'mmap.c',
   'signal.c',
   'strace.c',
-  'syscall.c',
   'uaccess.c',
 ))