This function lacks a declaration in header.h and isn't used
outside of this source file.

This fixes warnings about missing a prototype, when built as part
of mingw-w64-tools (where it is built with -Wmissing-prototypes).
Signed-off-by: Martin Storsjo <martin@martin.st>
Signed-off-by: Jacek Caban <jacek@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>