Introduce ERRNO_IS_FS_WRITE_REFUSED(), and use it in binfmt_mounted() (#38117)

- This introduces ERRNO_IS_FS_WRITE_REFUSED(), and apply it where
usable.
- This makes unexpected errors in access_fd() called by binfmt_mounted()
propagated to the caller.
- Renames binfmt_mounted() to binfmt_mounted_and_writable(), as it also
checks the fs is writable.
- Voidifies one disable_binfmt() call in shutdown.c.

src/basic/errno-util.h

@@ -188,6 +188,12 @@ static inline bool ERRNO_IS_NEG_PRIVILEGE(intmax_t r) {
 }
 _DEFINE_ABS_WRAPPER(PRIVILEGE);
 
+/* Three different errors for writing on a filesystem */
+static inline bool ERRNO_IS_NEG_FS_WRITE_REFUSED(intmax_t r) {
+        return r == -EROFS || ERRNO_IS_NEG_PRIVILEGE(r);
+}
+_DEFINE_ABS_WRAPPER(FS_WRITE_REFUSED);
+
 /* Three different errors for "not enough disk space" */
 static inline bool ERRNO_IS_NEG_DISK_SPACE(intmax_t r) {
         return IN_SET(r,