[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

llvm-svn: 218247