system/extra: include more of what you use.

This is a reland of aa24bc89b78a5981df7618bdef78b7b49ffad14d which was
reverted in 291e20dab39783c7074191ff2d2de9b86465c10f because it broke
the git_master-gpl builder.

This version of the change uses crypto.h as a proxy for mem.h because
it'll work in both BoringSSL and OpenSSL.

(cherry picked from commit a83adf6354f3073a1938ffcd6cadd5c357856de5)

Bug: 21085331
Change-Id: I9e4c9e4d459c2e31f74180b3a3b2ab139ab76e80
2 files changed