util: make lookup_uid() global

This is a useful helper, make it global. It will be required for
libsystemd-terminal, at minimum.

src/shared/util.c

@@ -2604,7 +2604,7 @@ bool hostname_is_set(void) {
         return !isempty(u.nodename) && !streq(u.nodename, "(none)");
 }
 
-static char *lookup_uid(uid_t uid) {
+char *lookup_uid(uid_t uid) {
         long bufsize;
         char *name;
         _cleanup_free_ char *buf = NULL;

src/shared/util.h

@@ -432,6 +432,7 @@ int sigprocmask_many(int how, ...);
 
 bool hostname_is_set(void);
 
+char* lookup_uid(uid_t uid);
 char* gethostname_malloc(void);
 char* getlogname_malloc(void);
 char* getusername_malloc(void);