This verifies that the <bits/extc++.h> header can be compiled with ASCII
as the input character set.
PR libstdc++/88607
* testsuite/17_intro/headers/c++1998/charset.cc: New test.
* testsuite/17_intro/headers/c++2011/charset.cc: New test.
* testsuite/17_intro/headers/c++2014/charset.cc: New test.
* testsuite/17_intro/headers/c++2017/charset.cc: New test.
* testsuite/17_intro/headers/c++2020/charset.cc: New test.
From-SVN: r267607