Update/Fix CMake build (#65)

Motivation:
SwiftPM's CMake build
(swiftlang/swift-package-manager#3202) unsuccessful
even with #60.

Modifications:
- Use consistent `SWIFT_CRYPTO_EXPORTS` naming. In some places `CRYPTO_EXPORTS` was used instead.
- Install `CCryptoBoringSSL` so we can import it in code (see swiftlang/swift-package-manager#3202)
- Always set `BUILD_SHARED_LIBS`

Result:
Successful CMake build.

Author: yim-lee

CMakeLists.txt

@@ -31,9 +31,7 @@ endif()
 set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin)
 set(CMAKE_Swift_MODULE_DIRECTORY ${CMAKE_BINARY_DIR}/swift)
 
-if(CMAKE_SYSTEM_NAME STREQUAL Windows OR CMAKE_SYSTEM_NAME STREQUAL Darwin)
-  option(BUILD_SHARED_LIBS "Build shared libraries by default" YES)
-endif()
+option(BUILD_SHARED_LIBS "Build shared libraries by default" YES)
 
 if(BUILD_SHARED_LIBS)
   set(CMAKE_POSITION_INDEPENDENT_CODE YES)

cmake/modules/CMakeLists.txt

@@ -12,9 +12,9 @@
 ##
 ##===----------------------------------------------------------------------===##
 
-set(CRYPTO_EXPORTS_FILE ${CMAKE_CURRENT_BINARY_DIR}/CryptoExports.cmake)
-configure_file(CryptoConfig.cmake.in
-    ${CMAKE_CURRENT_BINARY_DIR}/CryptoConfig.cmake)
+set(SWIFT_CRYPTO_EXPORTS_FILE ${CMAKE_CURRENT_BINARY_DIR}/SwiftCryptoExports.cmake)
+configure_file(SwiftCryptoConfig.cmake.in
+    ${CMAKE_CURRENT_BINARY_DIR}/SwiftCryptoConfig.cmake)
 
-get_property(CRYPTO_EXPORTS GLOBAL PROPERTY CRYPTO_EXPORTS)
-export(TARGETS ${CRYPTO_EXPORTS} FILE ${CRYPTO_EXPORTS_FILE})
+get_property(SWIFT_CRYPTO_EXPORTS GLOBAL PROPERTY SWIFT_CRYPTO_EXPORTS)
+export(TARGETS ${SWIFT_CRYPTO_EXPORTS} FILE ${SWIFT_CRYPTO_EXPORTS_FILE})

cmake/modules/CryptoConfig.cmake.in

@@ -0,0 +1,17 @@
+##===----------------------------------------------------------------------===##
+##
+## This source file is part of the SwiftCrypto open source project
+##
+## Copyright (c) 2021 Apple Inc. and the SwiftCrypto project authors
+## Licensed under Apache License v2.0
+##
+## See LICENSE.txt for license information
+## See CONTRIBUTORS.md for the list of SwiftCrypto project authors
+##
+## SPDX-License-Identifier: Apache-2.0
+##
+##===----------------------------------------------------------------------===##
+
+if(NOT TARGET SwiftCrypto)
+  include(@SWIFT_CRYPTO_EXPORTS_FILE@)
+endif()