This cleans up the parsing of MP_REGISTER_MODULE() and generation of
genhdr/moduledefs.h so that it uses the same process as compressed error
string messages, using the output of qstr extraction.
This makes sure all MP_REGISTER_MODULE()'s that are part of the build are
correctly picked up. Previously the extraction would miss some (eg if you
had a mod.c file in the board directory for an stm32 board).
Build speed is more or less unchanged.
Thanks to @stinos for the ports/windows/msvc/genhdr.targets changes.
Signed-off-by: Damien George <damien@micropython.org>