Enhance the 'Vectors and Extended Vectors' section.

Added cast operations to the table of vector operations. Supported status 'no' means that there are no tests in the Clang test suite for the given cast.
unique_ptrify IRObjectFile::createIRObjectFile

I took a guess at the changes to the gold plugin, because that doesn't
seem to build by default for me. Not sure what dependencies I might be
missing for that.