Reduce GNU Make latency 17% for cosmo

fgets() is now 4x faster which makes Make 2% faster. Landlock Make now
has a builtin $(uniq ...) function that uses critbit trees rather than
functional programming. Since uniq is the most important function this
optimization makes our cold start latency 15% faster.

third_party/make/expand.c

@@ -441,7 +441,8 @@ expand_argument (const char *str, const char *end)
 
   r = allocated_variable_expand (tmp);
 
-  free (alloc);
+  if (alloc)
+    free (alloc);
 
   return r;
 }