skipPast got confused when STACK_OF wasn't in the front of the string (which it
rarely was due to OPENSSL_EXPORT).

It also couldn't parse comments which end with a '*/' on their own.
(Stylistically we don't do this, but ssl_cipher_preference_list_st ends with an
ASCII art diagram which probably shouldn't gain a comment marker in the middle.)

Change-Id: I7687f4fd126003108906b995da0f2cd53f7d693a
Reviewed-on: https://boringssl-review.googlesource.com/4288
Reviewed-by: Adam Langley <agl@google.com>