vfs, swap: compile out IS_SWAPFILE() on swapless configs

No swap support -- no swapfiles possible.
Signed-off-by: Alexey Dobriyan (Yandex) <adobriyan@gmail.com>
Link: https://lore.kernel.org/r/2391c7f5-0f83-4188-ae56-4ec7ccbf2576@p183Signed-off-by: Christian Brauner <brauner@kernel.org>

include/linux/fs.h

@@ -2260,7 +2260,13 @@ static inline bool sb_rdonly(const struct super_block *sb) { return sb->s_flags
 
 #define IS_DEADDIR(inode)	((inode)->i_flags & S_DEAD)
 #define IS_NOCMTIME(inode)	((inode)->i_flags & S_NOCMTIME)
+
+#ifdef CONFIG_SWAP
 #define IS_SWAPFILE(inode)	((inode)->i_flags & S_SWAPFILE)
+#else
+#define IS_SWAPFILE(inode)	((void)(inode), 0U)
+#endif
+
 #define IS_PRIVATE(inode)	((inode)->i_flags & S_PRIVATE)
 #define IS_IMA(inode)		((inode)->i_flags & S_IMA)
 #define IS_AUTOMOUNT(inode)	((inode)->i_flags & S_AUTOMOUNT)