IRTests/InstructionsTest.cpp: Avoid initializer list.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204914 91177308-0d34-0410-b5e6-96231b3b80d8
SmallVector<3> may be used here.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@204915 91177308-0d34-0410-b5e6-96231b3b80d8