checkpatch: allow reporting C99 style comments

Presently C99 style comments are removed unconditionally before actual
patch validity check happens.  This is a problem for some third party
projects which use checkpatch.pl but do not allow C99 style comments.

This patch adds yet another variable, named C99_COMMENT_TOLERANCE.  If
it is included in the --ignore command line or config file options list,
C99 comments in the patch are reported as errors.

Tested by processing a patch with a C99 style comment, it passes the
check just fine unless '--ignore C99_COMMENT_TOLERANCE' is present in
.checkpatch.conf.

Link: http://lkml.kernel.org/r/20190110224957.25008-1-vbendeb@chromium.org
Signed-off-by: Vadim Bendebury <vbendeb@chromium.org>
Cc: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>