Revert "[libc++] Disable module_std and module_std_compat tests"

It looks like that broke the CI even more. Reverting until I can
investigate.

Author: ldionne

libcxx/test/libcxx/module_std.gen.py

@@ -18,9 +18,6 @@
 
 # RUN: %{python} %s %{libcxx-dir}/utils
 
-# TODO: Re-enable this test once we understand why it keeps timing out.
-# UNSUPPORTED: clang
-
 import sys
 
 sys.path.append(sys.argv[1])

libcxx/test/libcxx/module_std_compat.gen.py

@@ -18,9 +18,6 @@
 
 # RUN: %{python} %s %{libcxx-dir}/utils
 
-# TODO: Re-enable this test once we understand why it keeps timing out.
-# UNSUPPORTED: clang
-
 import sys
 
 sys.path.append(sys.argv[1])