[FileCheck] Use ASSERT for fatal unit tests

Summary:
A number of EXPECT statements in FileCheck's unit tests are dependent
from results of other values being tested. This commit changes those
earlier test to use ASSERT instead of EXPECT to avoid cascade errors
when they are all related to the same issue.

Reviewers: jhenderson, chandlerc, jdenny, probinson, grimar, arichardson, rnk

Subscribers: JonChesterfield, rogfer01, hfinkel, kristina, rnk, tra, arichardson, grimar, dblaikie, probinson, llvm-commits, hiraditya

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D64921

llvm-svn: 366862