Add shared lib target, rename static lib (fix #55)

Code using multiple copies of the static libraries in one process can
cause problems due to multiple copies of the protobuffer libraries not
interacting correctly. Change default target library to be a shared
library, add static variant as _static, and use object libraries to
optimize the building of the shared and _pic static libraries.

Author: pmai

CMakeLists.txt

@@ -25,22 +25,38 @@ set(OSI_PROTO_FILES
 
 protobuf_generate_cpp(PROTO_SRCS PROTO_HEADERS ${OSI_PROTO_FILES})
 
-add_library(${PROJECT_NAME} STATIC ${PROTO_SRCS} ${PROTO_HEADERS})
-target_include_directories(${PROJECT_NAME}
+add_library(${PROJECT_NAME}_static STATIC ${PROTO_SRCS} ${PROTO_HEADERS})
+target_include_directories(${PROJECT_NAME}_static
     PUBLIC
         ${PROTOBUF_INCLUDE_DIR}
         ${CMAKE_CURRENT_BINARY_DIR}
 )
-target_link_libraries(${PROJECT_NAME} PUBLIC ${PROTOBUF_LIBRARY})
+target_link_libraries(${PROJECT_NAME}_static PUBLIC ${PROTOBUF_LIBRARY})
+
+
+add_library(${PROJECT_NAME}_obj OBJECT ${PROTO_SRCS} ${PROTO_HEADERS})
+target_include_directories(${PROJECT_NAME}_obj
+    PUBLIC
+        ${PROTOBUF_INCLUDE_DIR}
+        ${CMAKE_CURRENT_BINARY_DIR}
+)
+set_property(TARGET ${PROJECT_NAME}_obj PROPERTY POSITION_INDEPENDENT_CODE ON)
 
 
-add_library(${PROJECT_NAME}_pic STATIC ${PROTO_SRCS} ${PROTO_HEADERS})
+add_library(${PROJECT_NAME}_pic STATIC $<TARGET_OBJECTS:${PROJECT_NAME}_obj>)
 target_include_directories(${PROJECT_NAME}_pic
     PUBLIC
         ${PROTOBUF_INCLUDE_DIR}
         ${CMAKE_CURRENT_BINARY_DIR}
 )
 target_link_libraries(${PROJECT_NAME}_pic PUBLIC ${PROTOBUF_LIBRARY})
+set_property(TARGET ${PROJECT_NAME}_pic PROPERTY POSITION_INDEPENDENT_CODE ON)
 
 
-set_property(TARGET ${PROJECT_NAME}_pic PROPERTY POSITION_INDEPENDENT_CODE ON)
+add_library(${PROJECT_NAME} SHARED $<TARGET_OBJECTS:${PROJECT_NAME}_obj>)
+target_include_directories(${PROJECT_NAME}
+    PUBLIC
+        ${PROTOBUF_INCLUDE_DIR}
+        ${CMAKE_CURRENT_BINARY_DIR}
+)
+target_link_libraries(${PROJECT_NAME} PUBLIC ${PROTOBUF_LIBRARY})