Unix/Process.inc: Revert r72332, "Work around a page size issue on Cygwin."

Offset in mmap(3) should be aligned to gepagesize(), 64k, or mmap(3) would fail.

TODO: Invetigate places where 4096 would be required as pagesize, or 4096 would satisfy.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@188903 91177308-0d34-0410-b5e6-96231b3b80d8