linux-user: protect fcntl64 with an #ifdef

Checking TARGET_ABI_BITS is sketchy - we should check for the presence
of the define to be sure. Also clean up the white space while we are
there.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20200403191150.863-3-alex.bennee@linaro.org>

linux-user/syscall.c

@@ -11331,7 +11331,7 @@ static abi_long do_syscall1(void *cpu_env, int num, abi_long arg1,
            This is a hint, so ignoring and returning success is ok.  */
         return 0;
 #endif
-#if TARGET_ABI_BITS == 32
+#ifdef TARGET_NR_fcntl64
     case TARGET_NR_fcntl64:
     {
         int cmd;