This is the full set of winapi headers from the mingw-64 project
from 2009/12/20 (gcc version 4.5.0 experimental).

A part of these files is already included (with minor modifications)
with the tcc-0.9.27 release.  Original versions of these files can
be found in the 'orig' folder.

The other files (from the 'include' folder) may be copied to the tcc
installation or used with -I or -isystem.

Compatibility with tcc has not been checked.  Do not expect everything
to work out of the box under all circumstances.
