[x32] Fix segmented stacks support

Summary:
Update segmented-stacks*.ll tests with x32 target case and make
corresponding changes to make them pass.

Test Plan: tests updated with x32 target

Reviewers: nadav, rafael, dschuff

Subscribers: llvm-commits, zinovy.nis

Differential Revision: http://reviews.llvm.org/D5245

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218247 91177308-0d34-0410-b5e6-96231b3b80d8