CMake: Export and install library targets.

The configs can be consumed by setting LibreSSL_DIR to the build
directory, or after installation using CMAKE_PREFIX_PATH/LibreSSL_DIR.

For compatibility, the EXPORT_NAME of targets and the LIBRESSL_*
variables are set to match the names used in FindLibreSSL.

ssl/CMakeLists.txt

@@ -91,9 +91,29 @@ if (WIN32)
 endif()
 set_target_properties(ssl PROPERTIES
 	OUTPUT_NAME ssl${SSL_POSTFIX}
-	ARCHIVE_OUTPUT_NAME ssl${SSL_POSTFIX})
-set_target_properties(ssl PROPERTIES VERSION ${SSL_VERSION}
-	SOVERSION ${SSL_MAJOR_VERSION})
+	ARCHIVE_OUTPUT_NAME ssl${SSL_POSTFIX}
+	EXPORT_NAME SSL
+	VERSION ${SSL_VERSION}
+	SOVERSION ${SSL_MAJOR_VERSION}
+)
+
+target_include_directories(
+	ssl
+	PUBLIC
+	$<BUILD_INTERFACE:${CMAKE_BINARY_DIR}/include>
+	$<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>
+)
+
+install(
+	TARGETS ssl
+	EXPORT SSL-target
+)
+
+export(
+	EXPORT SSL-target
+	FILE "${LibreSSL_BINARY_DIR}/LibreSSL-SSL.cmake"
+	NAMESPACE LibreSSL::
+)
 
 if(ENABLE_LIBRESSL_INSTALL)
 	install(
@@ -102,6 +122,12 @@ if(ENABLE_LIBRESSL_INSTALL)
 		LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
 		RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR}
 	)
+	install(
+		EXPORT SSL-target
+		FILE "LibreSSL-SSL.cmake"
+		NAMESPACE LibreSSL::
+		DESTINATION "${LIBRESSL_INSTALL_CMAKEDIR}/LibreSSL"
+	)
 endif(ENABLE_LIBRESSL_INSTALL)
 
 # build static library for regression test