Deduplicate error string patterns (#37676)

I wanted to see if moving moving out constant string arguments our of
error messages results in smaller binary sizes. Turns out it does, but
the savings are not consistent. Sometimes we get a few kB in a single
binary, sometimes there is no size change.

src/shared/mount-util.c

@@ -45,7 +45,7 @@ int umount_recursive_full(const char *prefix, int flags, char **keep) {
 
         f = fopen("/proc/self/mountinfo", "re"); /* Pin the file, in case we unmount /proc/ as part of the logic here */
         if (!f)
-                return log_debug_errno(errno, "Failed to open /proc/self/mountinfo: %m");
+                return log_debug_errno(errno, "Failed to open %s: %m", "/proc/self/mountinfo");
 
         for (;;) {
                 _cleanup_(mnt_free_tablep) struct libmnt_table *table = NULL;
@@ -454,7 +454,7 @@ int bind_remount_one(const char *path, unsigned long new_flags, unsigned long fl
 
         proc_self_mountinfo = fopen("/proc/self/mountinfo", "re");
         if (!proc_self_mountinfo)
-                return log_debug_errno(errno, "Failed to open /proc/self/mountinfo: %m");
+                return log_debug_errno(errno, "Failed to open %s: %m", "/proc/self/mountinfo");
 
         return bind_remount_one_with_mountinfo(path, new_flags, flags_mask, proc_self_mountinfo);
 }