checksyscalls: ignore fstat to silence build warning on LoongArch

fstat is replaced by statx on the new architecture, so an exception is
added to the checksyscalls script to silence the following build warning
on LoongArch:

CALL scripts/checksyscalls.sh
<stdin>:569:2: warning: #warning syscall fstat not implemented [-Wcpp]

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Tiezhu Yang <[e-mail]>
Suggested-by: WANG Xuerui <[e-mail]>
Suggested-by: Arnd Bergmann <[e-mail]>
Reviewed-by: Arnd Bergmann <[e-mail]>
Cc: Huacai Chen <[e-mail]>
Cc: Masahiro Yamada <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

scripts/checksyscalls.sh

···
 #define __IGNORE_truncate
 #define __IGNORE_stat
 #define __IGNORE_lstat
-#define __IGNORE_fstat
 #define __IGNORE_fcntl
 #define __IGNORE_fadvise64
 #define __IGNORE_newfstatat
···
 /* 64-bit ports never needed these, and new 32-bit ports can use statx */
 #define __IGNORE_fstat64
 #define __IGNORE_fstatat64
+
+/* Newer ports are not required to provide fstat in favor of statx */
+#define __IGNORE_fstat
 EOF
 }