Simplify all the cipher gathering logic. The set of supported ciphers is known,
so there is no need to determine if some cipher exists but doesn't work.

Change-Id: Idcaae67e7bfc40a3deb925d85ee1a99a931b67e7
Reviewed-on: https://boringssl-review.googlesource.com/1756
Reviewed-by: Adam Langley <agl@google.com>

Chromium does not like static initializers, and the CPU logic uses one to
initialize CPU bits. However, the crypto library lacks an explicit
initialization function, which could complicate (no compile-time errors)
porting existing code which uses crypto/, but not ssl/.

Add an explicit CRYPTO_library_init function, but make it a no-op by default.
It only does anything (and is required) if building with
BORINGSSL_NO_STATIC_INITIALIZER.

Change-Id: I6933bdc3447fb382b1f87c788e5b8142d6f3fe39
Reviewed-on: https://boringssl-review.googlesource.com/1770
Reviewed-by: Adam Langley <agl@google.com>

Initial fork from f2d678e6e8 (1.0.2 beta).

(This change contains substantial changes from the original and
effectively starts a new history.)