We don't use "final" in our code, as very few classes in wx code have
virtual functions but are not meant to be derived from in the user code.
Ideal would be to check the existing warnings and maybe apply "final" if
it's relevant and disable it otherwise, as these warnings can be useful
to build the application code with, but for now just disable them in the
test suite.
As wx headers are included from user applications which may compile with
higher warning level than wx itself, try to check headers compilation
with almost all of gcc warning flags turned on.
This notably should prevent the headers from becoming uncompilable with
-pedantic again in the future.
Check that all our public headers compile with this macro defined and
that using a char string without specifying its expected encoding
results in the expected compilation failure in this case.
