cmake: add missing define to routing build for msvc

Author: Mizux

ortools/routing/CMakeLists.txt

@@ -20,6 +20,10 @@ add_library(${NAME} OBJECT ${_SRCS})
 set_target_properties(${NAME} PROPERTIES
   POSITION_INDEPENDENT_CODE ON
   )
+if(MSVC AND BUILD_SHARED_LIBS)
+  target_compile_definitions(${NAME} PUBLIC "OR_BUILD_DLL")
+  target_compile_definitions(${NAME} PRIVATE "OR_EXPORT")
+endif()
 target_include_directories(${NAME} PRIVATE
   ${PROJECT_SOURCE_DIR}
   ${PROJECT_BINARY_DIR})