Fix makefile for debuginfo-tests execution.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@220112 91177308-0d34-0410-b5e6-96231b3b80d8
Append the %itanium_abi_host_triple substitution unconditionally

We will fail if it's not set, even if we don't substitute.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@220114 91177308-0d34-0410-b5e6-96231b3b80d8