cl/gcc-adapt: Support for using g++ for debugging added.

'cc1' is still used by default. Use the 'run-test-cc1plus' script for
running g++ with the Code Listener.
cl/gcc-adapt-ext: Test-cases for basic C constructs support added.
cl/gcc-adapt-ext: Test-cases for basic C constructs support added.
cl/gcc-adapt-ext: basic support for constructors & destructors added

This is actually support for processing of METHOD_TYPE node, which
might change in future. The RECORD_TYPE node is still unhandled.
cl/gcc-adapt-ext: Test suite fixed to run 'cc1plus' again for C++ tests.