[test] Add --failfast flag to test runner (WebAssembly#1747)

Author: sbc100

test/core/run.py

@@ -19,6 +19,7 @@
 parser.add_argument("--wasm", metavar="<wasm-command>", default=os.path.join(interpDir, "wasm"))
 parser.add_argument("--js", metavar="<js-command>")
 parser.add_argument("--generate-js-only", action='store_true')
+parser.add_argument("--failfast", action='store_true')
 parser.add_argument("--out", metavar="<out-dir>", default=outputDir)
 parser.add_argument("file", nargs='*')
 arguments = parser.parse_args()
@@ -117,4 +118,4 @@ def _runTestFile(self, inputPath):
   for fileName in inputFiles:
     testName = 'test ' + os.path.basename(fileName)
     setattr(RunTests, testName, lambda self, file=fileName: self._runTestFile(file))
-  unittest.main()
+  unittest.main(failfast=arguments.failfast)