Add time to GC tracing.

src/wren_common.h

@@ -43,6 +43,9 @@
 // Set this to true to log memory operations as they occur.
 #define WREN_TRACE_MEMORY false
 
+// Set this to true to log garbage collections as they occur.
+#define WREN_TRACE_GC false
+
 // The maximum number of arguments that can be passed to a method. Note that
 // this limtation is hardcoded in other places in the VM, in particular, the
 // `CODE_CALL_XX` instructions assume a certain maximum number.