Chromium's doesn't have built-in support for ml64.exe. Seems easier to
just build consistently with Yasm on both Win32 and Win64. (This will
require an equivalent change in Chromium's build, but keep upstream
and downstream builds consistent.)

Also don't set CMAKE_ASM_NASM_COMPILER explicitly; cmake's default
ASM_NASM behavior will search for both nasm or yasm in %PATH%. Leave
it unset so it can be overwritten on the command-line to point to
a particular yasm. Update BUILDING accordingly.

Verified the tests still pass.

Change-Id: I7e434be474b5b2d49e3bafbced5b41cc0246bd00
Reviewed-on: https://boringssl-review.googlesource.com/2104
Reviewed-by: Adam Langley <agl@google.com>

OBJECT library types are supported only in CMake 2.8.8 or higher, and
attempting to build BoringSSL on Ubuntu 12.04 results in CMake
displaying unhelpful error messages.

Change-Id: I2bc77a2c95d4f6ee41f8489ff679a2a0ba48c508
Reviewed-on: https://boringssl-review.googlesource.com/1530
Reviewed-by: Adam Langley <agl@google.com>

This change marks public symbols as dynamically exported. This means
that it becomes viable to build a shared library of libcrypto and libssl
with -fvisibility=hidden.

On Windows, one not only needs to mark functions for export in a
component, but also for import when using them from a different
component. Because of this we have to build with
|BORINGSSL_IMPLEMENTATION| defined when building the code. Other
components, when including our headers, won't have that defined and then
the |OPENSSL_EXPORT| tag becomes an import tag instead. See the #defines
in base.h

In the asm code, symbols are now hidden by default and those that need
to be exported are wrapped by a C function.

In order to support Chromium, a couple of libssl functions were moved to
ssl.h from ssl_locl.h: ssl_get_new_session and ssl_update_cache.

Change-Id: Ib4b76e2f1983ee066e7806c24721e8626d08a261
Reviewed-on: https://boringssl-review.googlesource.com/1350
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.)