Restore lit feature object-emission. Omit DebugInfo/Generic on XCore.

D73568 removed the lit feature object-emission, because it was introduced for a
target which did not support the integrated assembler, and that target no longer
required the feature. XCore still does not support the integrated assembler,
so a build with XCore as the default target fails tests requiring
object-emission. This issue was not publicly visible because there was not a
buildbot for XCore as the default target. We fixed the failures downstream. We
now have builder clang-xcore-ubuntu-20-x64 on the staging buildmaster, which
shows the failures. We would like to make upstream build green.

Omit DebugInfo/Generic on XCore to avoid annotating 70 separate files.

Differential Revision: https://reviews.llvm.org/D98508