[Test][DebugInfo] Check for backend object emission support.
The XCore backend does not support object emission. Several tests fail for this
reason when XCore is the default target. See staging buildbot builder:
So check for backend object emission before running the tests requiring it.
Incorporate isConfigurationSupported functionality in isObjectEmissionSupported,
to avoid calling them both in the same tests.
Differential Revision: https://reviews.llvm.org/D98400