Fixed some problems with the logic of parsing line comments by adding

Fixed some problems with the logic of parsing line comments by adding
isAtStartOfComment and using that instead in two places where a loop
to check if the char was in MAI.getCommentString().

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@82059 91177308-0d34-0410-b5e6-96231b3b80d8