Allow comments in exported symbols response files.

It can be useful to have comments in a response file for exported
symbols to explain what some stuff might be in there for.

Author: waywardmonkeys

docs/emcc.txt

@@ -147,6 +147,9 @@ Options that are modified or new in *emcc* are listed below:
 
      * The specified file path must be absolute, not relative.
 
+     * The file may contain comments where the first character of the
+       line is `'#'`.
+
    Note:
 
      Options can be specified as a single argument with or without a

emcc.py

@@ -1450,7 +1450,7 @@ def parse_symbol_list_file(contents):
   kind of quoting or escaping.
   """
   values = contents.splitlines()
-  return [v.strip() for v in values]
+  return [v.strip() for v in values if not v.startswith('#')]
 
 
 def parse_value(text, expected_type):

test/test_other.py

@@ -7685,6 +7685,10 @@ def test_dash_s_response_file_list(self):
     self.run_process([EMCC, test_file('hello_world.c'), '-sEXPORTED_FUNCTIONS=@response_file.txt'])
     self.run_process([EMCC, test_file('hello_world.c'), '-sEXPORTED_FUNCTIONS=@response_file.json'])
 
+  def test_dash_s_response_file_list_with_comments(self):
+    create_file('response_file.txt', '_main\n#_nope_ish_nope\n_malloc\n')
+    self.run_process([EMCC, test_file('hello_world.c'), '-sEXPORTED_FUNCTIONS=@response_file.txt'])
+
   def test_dash_s_response_file_misssing(self):
     err = self.expect_fail([EMCC, test_file('hello_world.c'), '-sEXPORTED_FUNCTIONS=@foo'])
     self.assertContained('error: foo: file not found parsing argument: EXPORTED_FUNCTIONS=@foo', err)