Add build configuration for CPP static library

The CPP static library respects options
BUILD_STATIC_LIBRARY and WITH_PIC as well.

Signed-off-by: Lance Chen <cyen0312@gmail.com>

lib/cpp/CMakeLists.txt

@@ -2,8 +2,14 @@ include_directories(${mosquitto_SOURCE_DIR}/lib ${mosquitto_SOURCE_DIR}/lib/cpp
 			${STDBOOL_H_PATH} ${STDINT_H_PATH})
 link_directories(${mosquitto_BINARY_DIR}/lib)
 
-add_library(mosquittopp SHARED
-	mosquittopp.cpp mosquittopp.h)
+set(C_SRC mosquittopp.cpp mosquittopp.h)
+
+add_library(mosquittopp_obj OBJECT ${C_SRC})
+set_target_properties(mosquittopp_obj PROPERTIES
+	POSITION_INDEPENDENT_CODE 1
+)
+
+add_library(mosquittopp SHARED $<TARGET_OBJECTS:mosquittopp_obj>)
 
 target_link_libraries(mosquittopp libmosquitto)
 set_target_properties(mosquittopp PROPERTIES
@@ -11,6 +17,31 @@ set_target_properties(mosquittopp PROPERTIES
 	SOVERSION 1
 )
 install(TARGETS mosquittopp RUNTIME DESTINATION ${BINDIR} LIBRARY DESTINATION ${LIBDIR})
+
+if (${BUILD_STATIC_LIBRARY} STREQUAL ON)
+	if (${WITH_PIC} STREQUAL OFF)
+		add_library(mosquittopp_static STATIC
+			$<TARGET_OBJECTS:libmosquitto_obj>
+			${C_SRC}
+		)
+	else (${WITH_PIC} STREQUAL OFF)
+		add_library(mosquittopp_static STATIC
+			$<TARGET_OBJECTS:libmosquitto_obj>
+			$<TARGET_OBJECTS:mosquittopp_obj>
+		)
+	endif (${WITH_PIC} STREQUAL OFF)
+
+	target_link_libraries(mosquittopp_static ${LIBRARIES})
+
+	set_target_properties(mosquittopp_static PROPERTIES
+		OUTPUT_NAME mosquittopp
+		VERSION ${VERSION}
+	)
+
+	target_compile_definitions(mosquittopp_static PUBLIC "LIBMOSQUITTO_STATIC")
+	install(TARGETS mosquittopp_static RUNTIME DESTINATION ${BINDIR} ARCHIVE DESTINATION ${LIBDIR})
+endif (${BUILD_STATIC_LIBRARY} STREQUAL ON)
+
 install(FILES mosquittopp.h DESTINATION ${INCLUDEDIR})
 
 if (UNIX AND NOT APPLE)