build: add test-gc-clean and test-gc PHONY rules

Author: joyeecheung

Makefile

@@ -309,6 +309,9 @@ clear-stalled:
 test-gc: all test/gc/build/Release/binding.node
 $(PYTHON) tools/test.py --mode=release gc
 
+test-gc-clean:
+$(RM) -r test/gc/build
+
 test-build: | all build-addons build-addons-napi
 
 test-build-addons-napi: all build-addons-napi
@@ -963,6 +966,8 @@ endif
  test-ci \
  test-ci-js \
  test-ci-native \
+ test-gc \
+ test-gc-clean \
  test-v8 \
  test-v8-all \
  test-v8-benchmarks \