[NFC] [FileCheck] Fix init of stack objects in unit tests

Summary:
Fix initialization style of objects allocated on the stack in unit test
to use the "Type Var(init list)" convention.

Reviewers: jhenderson, probinson, arichardson, grimar, jdenny

Subscribers: llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D68425

llvm-svn: 373717