only slot :0 provides headers... I guess they are needed during compilation?
Makefile:16: SHA1_HEADER = <openssl/sha.h>
+ 21 May 2014; Sergey Popov <pinkbyte@gentoo.org> cgit-0.10.1.ebuild, + cgit-9999.ebuild: + QA: add slot to openssl dependency, wrt bug #508174. Thanks to Julian Ospald + for discovering this issue