simplify CMakeList with cmake scripts

build/cmake/shared_libs.cmake

@@ -0,0 +1,30 @@
+    if(WIN32)
+        set(CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS ON)
+        if(MSVC)
+            set(DLLTOOL OFF)
+        else()
+            # mingw: If dlltool is found the def and lib file will be created
+            find_program (DLLTOOL dlltool)
+            if(NOT DLLTOOL)
+                message(WARNING "dlltool not found. Skipping import library generation.")
+            endif()
+        endif()
+        if(DLLTOOL)
+            #generate the lib and def files needed by msvc
+            set_target_properties (nana   PROPERTIES
+                    OUTPUT_NAME         nana
+                    ARCHIVE_OUTPUT_NAME nana
+                    LINK_FLAGS "${CMAKE_SHARED_LINKER_FLAGS_INIT} -Wl,--output-def=${CMAKE_CURRENT_BINARY_DIR}/libnana.def"
+                    )
+
+            add_custom_command(TARGET nana POST_BUILD
+                    WORKING_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}"
+                    COMMAND echo "       Generating import library"
+                    COMMAND "${DLLTOOL}" --dllname    "libnana.dll"
+                    --input-def  "libnana.def"
+                    --output-lib "libnana.lib")
+
+            install(FILES "${CMAKE_CURRENT_BINARY_DIR}/libnana.def"
+                    "${CMAKE_CURRENT_BINARY_DIR}/libnana.lib" DESTINATION lib)
+        endif()
+    endif()