Add flag to skip integrated driver tests (swiftlang#2884)

This can be used in cases where the compiler being used isn't compatible
with the integrated driver. By default, we will still run the test with
the integrated driver as well.

Author: neonichu

Utilities/bootstrap

@@ -130,6 +130,11 @@ def add_build_args(parser):
         help="paths (relative to the project root) where to install build products [%(default)s]",
         default=["/tmp/swiftpm"],
         metavar="PATHS")
+    parser.add_argument(
+        "--skip-integrated-driver-tests",
+        action="store_true",
+        help="whether to skip tests with the integrated driver",
+        default=True)
 
 def add_test_args(parser):
     """Configures the parser with the arguments necessary for the test action."""
@@ -303,6 +308,9 @@ def test(args):
     # Test SwiftPM.
     call_swiftpm(args, cmd)
 
+    if args.skip_integrated_driver_tests:
+        return
+
     # Build SwiftPM with the integrated driver.
     note("Bootstrap with the integrated Swift driver")
     build_swiftpm_with_swiftpm(args,integrated_swift_driver=True)