[Vala] discarded qualifiers warnings

[Adam Dingle <adam yorba org>]

When building any substantial Vala program, gcc outputs lots of warnings 
like these as it processes the C code generated by valac:

warning: assignment discards qualifiers from pointer target type
warning: passing argument 1 of ‘foo’ discards qualifiers from pointer 
target type

These warnings arise from const/non-const mismatches. In a large Vala 
program, there are so many warnings like this that programmers typically 
don't look at the compiler output at all, making all warnings useless.

It seems that making all these warnings go away will be a non-trivial 
effort for Vala and may take quite some time (I spoke briefly with Jürg 
about this at GUADEC a couple of months ago). In the meantime, it would 
be great to have a GCC option to suppress discarded qualifiers warnings. 
Unfortunately there is no such option today, but I just filed a GCC 
enhancement request:

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41215

Patches welcome. :)

adam