[build_script.py] Remove redundant argparse params

- For options `like-this`, `argparse` stores the variable name
  `like_this`. Remove redundant `dest` parameters in the build script.
- For options marked as "store", `argparse` stores `None` when the
  option is not specified. Remove redudnant `default=None` parameters
  in the build script.
- For options marked as "store_true", the default value is `False`.
  Remove redundant `default=True` parameters in the build script.
- The default action for options is "store". Remove redundant
  `action="store"` parameters in the build script.

Author: modocache

build_script.py

@@ -29,36 +29,23 @@ def main():
     parser.add_argument("--swiftc",
                         help="path to the swift compiler",
                         metavar="PATH",
-                        action="store",
-                        dest="swiftc",
-                        required=True,
-                        default=None)
+                        required=True)
     parser.add_argument("--build-dir",
                         help="path to the output build directory",
                         metavar="PATH",
-                        action="store",
-                        dest="build_dir",
-                        required=True,
-                        default=None)
+                        required=True)
     parser.add_argument("--swift-build-dir",
                         help="path to the swift build directory",
                         metavar="PATH",
-                        action="store",
-                        dest="swift_build_dir",
-                        required=True,
-                        default=None)
+                        required=True)
     parser.add_argument("--module-install-path",
                         help="location to install module files",
                         metavar="PATH",
-                        action="store",
-                        dest="module_path",
-                        default=None)
+                        dest="module_path")
     parser.add_argument("--library-install-path",
                         help="location to install shared library files",
                         metavar="PATH",
-                        action="store",
-                        dest="lib_path",
-                        default=None)
+                        dest="lib_path")
     parser.add_argument("--release",
                         help="builds for release",
                         action="store_const",
@@ -78,9 +65,7 @@ def main():
                              "at {} in order to run this command. ".format(
                                  os.path.join(
                                      os.path.dirname(SOURCE_DIR), 'llvm')),
-                        action="store_true",
-                        dest="test",
-                        default=False)
+                        action="store_true")
     args = parser.parse_args()
 
     swiftc = os.path.abspath(args.swiftc)