RFC: add a testsuite for libstdc++ pretty-printers

[Tom Tromey]

Tom> * testsuite/libstdc++-pp/simple.cc: New file.
Tom> * testsuite/lib/gdb-test.exp: New file.
Tom> * testsuite/libstdc++-pp/pp.exp: New file.

Benjamin> feel free to spell out prettyprinters instead of using pp, if you want
Benjamin> to make it very obvious what is going on in this directory.

Benjamin> we really strive for clarity given that this testsuite is so large

No problem, I will do that.

Jonathan> This should also help us notice if we rely on features of a
Jonathan> particular version of python or gdb which fail with earlier
Jonathan> versions, e.g. python 2.6 conditional expressions and gdb 7.1
Jonathan> lazy strings.

Benjamin> Yep. Testresults should be very interesting to watch.

One potential problem is that gdb may change formatting details, causing
spurious failures.  I don't think that is a very big problem though.
For one thing, we can always change the dg-final annotations to use
regexps.

Tom