There is no need to use `--check-prefix` multiple times.
It helps to improve readability/test maintainability.
This patch does it for all tools at once.
Differential revision: https://reviews.llvm.org/D78217
Pulling out the split-dwarf tests by way of example of how I think
llvm-symbolizer should be tested going forward. Open to
debate/discussion, though.
llvm-svn: 352004