Add -eventfd flag support to configure.exe

The lack of eventfd(7) switches and auto detection
caused cross-compilations to fail on Windows hosts,
for builds targeting POSIX systems which do
not support eventfd(7), such as QNX and BB10.

Change-Id: Ic8f53c64066ece6f16d4dbc79c089b058401e632
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>