tags: Treat header files as C code

This allows to apply the same patters to both source and header files.
The effect is mostly visible in the case of DECLARE_BITMAP, but there
are small gains all over the place. There is also lots of random changes
in the diff, I believe this is simply because there are still lots of
unexpanded macros in the code and the C and C++ parsers fail and recover
at different points. Also, qconf.h is parsed as C, but that's a
negligible regression.

Signed-off-by: Michal Marek <mmarek@suse.com>