* Disable testing the old mingw32 - it's too broken.
* Add feature dependency checks for new C++11 tests.
* Disable some tests that generate too large object files.
* Disable one concept check for gcc 6.2 which generates an internal compiler error.
* Increase expected error rate on one barycentric test - it was too tight to test on some platforms.
* Fix some __float128 miss-configurations.
