common-mingw: force ac_cv_func_mmap_fixed_mapped=no

common-mingw: force ac_cv_func_mmap_fixed_mapped=no

The expat mingw build breaks because ix86-common defines
ac_cv_func_mmap_fixed_mapped=yes, causing the build to think that
mmap(), mman.h actually exist. Fix this by always forcing the variable
to "no", which configure would have concluded without such interference.

(From OE-Core rev: 9add830b85222b57774acc35539e678d9ca8efb2)

Signed-off-by: Richard Tollerton <rich.tollerton@ni.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>