use geteuid syscall as well

src/ugid_linux.hpp

@@ -36,8 +36,8 @@ namespace mergerfs
       SetResetGuard(const uid_t _newuid,
                     const gid_t _newgid)
       {
-        olduid   = ::geteuid();
-        oldgid   = ::getegid();
+        olduid = ::syscall(SYS_geteuid);
+        oldgid = ::syscall(SYS_getegid);
         newuid = _newuid;
         newgid = _newgid;