lib/Target/SubtargetFeature.cpp asserts that the FeatureKV[] table be sorted

lib/Target/SubtargetFeature.cpp asserts that the FeatureKV[] table be sorted
by its first field, but TableGen doesn't actually enforce creating it that
way. TableGen sorts the records that will be used to create it by the names
of the records, not the Name field of those records.

This patch corrects the sort to use the "Name" field of the record as the
sort key.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@56106 91177308-0d34-0410-b5e6-96231b3b80d8