Bug 1578776 - wrap some synchronization-related STL headers; r=firefox-build-system-reviewers,mshal

I'm not sure how things have worked without these headers getting
wrapped, but they need to be for declarations in them to work properly.

Differential Revision: https://phabricator.services.mozilla.com/D44690

--HG--
extra : moz-landing-system : lando

config/stl-headers.mozbuild

@@ -26,6 +26,7 @@ stl_headers = [
     'cassert',
     'climits',
     'cmath',
+    'condition_variable',
     'cstdarg',
     'cstdio',
     'cstdlib',
@@ -42,9 +43,11 @@ stl_headers = [
     'list',
     'map',
     'memory',
+    'mutex',
     'ostream',
     'regex',
     'set',
+    'shared_mutex',
     'stack',
     'string',
     'thread',