fix(build): Fix running build scripts on Windows.

Fixes #2988

Change-Id: I09b1fad048da5172281db52cc0e2b615955a2b19

build/compiler.py

@@ -243,7 +243,8 @@ def generate(self, force=False):
 
     def_generator = _get_source_path('build/generateTsDefs.py')
 
-    cmd_line = [def_generator, '--output', self.output]
+    cmd_line = [sys.executable or 'python', def_generator, '--output',
+                self.output]
     cmd_line += self.source_files
 
     if shakaBuildHelpers.execute_get_code(cmd_line) != 0:

build/shakaBuildHelpers.py

@@ -144,6 +144,13 @@ def execute_subprocess(args, **kwargs):
   Returns:
     The same value as subprocess.Popen.
   """
+  # Windows can't run scripts directly, even if executable.  We need to
+  # explicitly run the interpreter.
+  if args[0].endswith('.js'):
+    raise ValueError('Use "node" to run JavaScript scripts')
+  if args[0].endswith('.py'):
+    raise ValueError('Use sys.executable to run Python scripts')
+
   if os.environ.get('PRINT_ARGUMENTS'):
     logging.info(' '.join([quote_argument(x) for x in args]))
   try: