stat-util: add statx_mount_same() to check if two stax refer to the same mount

src/basic/stat-util.h

@@ -74,6 +74,7 @@ bool stat_inode_same(const struct stat *a, const struct stat *b);
 bool stat_inode_unmodified(const struct stat *a, const struct stat *b);
 
 bool statx_inode_same(const struct statx *a, const struct statx *b);
+bool statx_mount_same(const struct new_statx *a, const struct new_statx *b);
 
 int statx_fallback(int dfd, const char *path, int flags, unsigned mask, struct statx *sx);