Omitting the extern storage qualifier when declaring a global variable in
a header file is mistake. If that header is included by several files it
results in multiple definitions of the same variable (unless -fcommon is
specified or assumed, the latter being the case for GCC 9.x and earlier).

This fixes building with GCC 10.
Signed-off-by: Gerald Pfeifer <gerald@pfeifer.com>
Signed-off-by: Hans Leidekker <hans@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>