Under certain versions of cygwin it appears PAGE_SIZE is already defined.
So change name to stop any possible build issues.
Change-Id: I6f0e0c352c06bb6118ac3a5b884ae8e93194b570
Signed-off-by: Spencer Oliver <spen@spen-soft.co.uk>
Reviewed-on: http://openocd.zylin.com/1675
Tested-by: jenkins