mm: shmem: avoid build warning for CONFIG_SHMEM=n

The newly added 'flags' variable is unused and causes a warning if
CONFIG_SHMEM is disabled, since the shmem_acct_size() macro it is passed
into does nothing:

mm/shmem.c: In function '__shmem_file_setup':
mm/shmem.c:5816:23: error: unused variable 'flags' [-Werror=unused-variable]
 5816 |         unsigned long flags = (vm_flags & VM_NORESERVE) ? SHMEM_F_NORESERVE : 0;
      |                       ^~~~~

Replace the two macros with equivalent inline functions to get the
argument checking.

Link: https://lkml.kernel.org/r/20251204102905.1048000-1-arnd@kernel.org
Fixes: 6ff1610 ("mm: shmem: use SHMEM_F_* flags instead of VM_* flags")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: David Hildenbrand (Red Hat) <david@kernel.org>
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Pratyush Yadav <pratyush@kernel.org>
Reviewed-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: guoweikang <guoweikang.kernel@gmail.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Kairui Song <kasong@tencent.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: arndb

mm/shmem.c

@@ -5799,8 +5799,15 @@ EXPORT_SYMBOL_GPL(shmem_truncate_range);
 #define shmem_vm_ops				generic_file_vm_ops
 #define shmem_anon_vm_ops			generic_file_vm_ops
 #define shmem_file_operations			ramfs_file_operations
-#define shmem_acct_size(flags, size)		0
-#define shmem_unacct_size(flags, size)		do {} while (0)
+
+static inline int shmem_acct_size(unsigned long flags, loff_t size)
+{
+	return 0;
+}
+
+static inline void shmem_unacct_size(unsigned long flags, loff_t size)
+{
+}
 
 static inline struct inode *shmem_get_inode(struct mnt_idmap *idmap,
 				struct super_block *sb, struct inode *dir,