Revert r205436:

        Extend the SSE2 comment lexing to AVX2. Only 16byte align when not on AVX2.

        This provides some 3% speedup when preprocessing gcc.c as a single file.


The patch is wrong, it always uses SSE2, and when I fix that there's no speedup
at all. I am not sure where the 3% came from previously.

--Thi lie, and those below, will be ignored--

M    Lex/Lexer.cpp