Add call to malloc_trim on a full GC

src/gc.c

@@ -6,6 +6,9 @@
 
 #include <string.h>
 #include <stdlib.h>
+#ifdef HAS_MALLOC_TRIM
+#include <malloc.h>
+#endif
 #include <mruby.h>
 #include <mruby/array.h>
 #include <mruby/class.h>
@@ -1319,6 +1322,9 @@ mrb_full_gc(mrb_state *mrb)
     gc->full = FALSE;
   }
 
+#ifdef HAS_MALLOC_TRIM
+  malloc_trim(0);
+#endif
   GC_TIME_STOP_AND_REPORT;
 }