[DWARF] - Simplify HandleExpectedError implementation in DWARFDebugInfoTest

Current implementation looks a bit confusing. It looks like it should
report/print something on error, but it does not do that.
It silently drops a error message when creating triple, though
this behavior is fine generally.

For example if LLVM configured with -DLLVM_TARGETS_TO_BUILD=ARM and
our host is windows, it is expected that we will be unable to
create "i386-pc-windows-msvc" target.

Patch introduces isConfigurationSupported() function that checks
if current configuration is supported for each test and returns early if not.

llvm-svn: 306812