libstdc++/69406 Fix test to check for supported headers
PR libstdc++/69406
* include/bits/cpp_type_traits.h: Ensure C++ language linkage.
* include/ext/type_traits.h: Likewise.
* testsuite/17_intro/headers/c++2011/linkage.cc: Check autoconf macros
for presence of C headers.
* testsuite/ext/type_traits/add_unsigned_floating_neg.cc: Adjust
dg-error line number.
* testsuite/ext/type_traits/add_unsigned_integer_neg.cc: Likewise.
* testsuite/ext/type_traits/remove_unsigned_floating_neg.cc: Likewise.
* testsuite/ext/type_traits/remove_unsigned_integer_neg.cc: Likewise.
git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@232672
138bc75d-0d04-0410-961f-
82ee72b054a4