Bug 1192278 - empower |make check-jit-test| to specify a subset of tests to run; r=terrence

Calling:

  make check-jit-test JITTEST_TEST_ARGS=basic/

will now run all tests whose name includes "basic/".  Similarly, running:

  make check-jit-test JITTEST_TEST_ARGS=basic/timeout-check.js

will run only basic/timeout-check.js.

js/src/Makefile.in

@@ -118,7 +118,7 @@ check-jit-test::
 	        --no-slow --no-progress --format=automation --jitflags=all \
 			$(JITTEST_VALGRIND_FLAG) \
 			$(JITTEST_EXTRA_ARGS) \
-	        $(DIST)/bin/$(JS_SHELL_NAME)$(BIN_SUFFIX)
+	        $(DIST)/bin/$(JS_SHELL_NAME)$(BIN_SUFFIX) $(JITTEST_TEST_ARGS)
 
 check:: check-style check-masm