__STDC_VERSION__ isn't defined for __cplusplus, so we've been removing
such checks. Some got missed.
Stop defining __func__ and just use the __PRETTY_FUNCTION__ GCC extension
in <assert.h>. Also fix the #if there so that C++ gets __assert2 rather
than __assert, and rewrite the cast to work with -I rather than -isystem.
Also remove __restrict and just always use the __restrict GCC extension.
Add a trivial test for <assert.h>.
Bug: http://b/30353757
Change-Id: Ie49bb417976293d3a9692b516e28fe3c0ae0a6d9
Test: ran bionic unit tests.
