Don't munch /* and */ comment start and end markers.

Don't munch /* and */ comment start and end markers.

In Sandro Sigala's original c-c++-grammars code, this function
was known as "static void skip_comment(void)". It was built this
way instead of a lex pattern because it didn't need to save the
matched comment in the "yytext" buffer. This is still true as
we directly assign the matched comment to the scanner object.
So simply prepend and append the markers back where they belong.

https://bugzilla.gnome.org/show_bug.cgi?id=672254