Print statistics for each record kind saying the number of bits

and % abbreviated.  For example:

	Record Histogram:
		  Count    # Bits   % Abv  Record Kind
		  25738   3424174  100.00  SM_SLOC_INSTANTIATION_ENTRY
		    814    562079  100.00  SM_SLOC_FILE_ENTRY
		    798     34110          SM_HEADER_FILE_INFO
		      3     91104  100.00  SM_SLOC_BUFFER_BLOB
		      3       498  100.00  SM_SLOC_BUFFER_ENTRY
		      1       465          SM_LINE_TABLE

llvm-svn: 70215