[PGO] Use rsplit to parse value-data line in text profile file.

The value-data line is <PGOFuncName>:<Count_Value>. PGOFuncName might contain
':' for the internal linkage functions. We therefore need to use rsplit,
rather split, to extract the data from the line. This fixes the error when
merging a text profile file to an indexed profile file.

llvm-svn: 268818