Add visibility rules.

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>
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 1e0ab07..d8a4e1b 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -10,6 +10,8 @@
 	set(CMAKE_C_FLAGS "/wd4267")
 endif()
 
+add_definitions(-DBORINGSSL_IMPLEMENTATION)
+
 if (${CMAKE_SYSTEM_PROCESSOR} STREQUAL "x86_64")
 	set(ARCH "x86_64")
 elseif (${CMAKE_SYSTEM_PROCESSOR} STREQUAL "amd64")