DWARFRecordSectionSplitter pre-builds a splitBlock cache, but wasn't passing it
to the call to splitBlock. This was an oversight in the original patch.
With 229d576b31f4071ab68c85ac4fabb78cfa502b04 the class EHFrameSplitter was renamed to DWARFRecordSectionSplitter. This change merely moves it to it's own .cpp/.h file
Differential Revision: https://reviews.llvm.org/D121721