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>