Fix export errors with MinGW

src/CMakeLists.txt

@@ -105,10 +105,6 @@ ADD_LIBRARY(lmmsobjs OBJECT
 GENERATE_EXPORT_HEADER(lmmsobjs
 	BASE_NAME lmms
 )
-# GENERATE_EXPORT_HEADER doesn't seem to do this automatically
-TARGET_COMPILE_DEFINITIONS(lmmsobjs
-	PRIVATE -Dlmmsobjs_EXPORTS
-)
 
 ADD_EXECUTABLE(lmms
 	core/main.cpp
@@ -119,6 +115,14 @@ TARGET_INCLUDE_DIRECTORIES(lmms
 	PUBLIC ${CMAKE_CURRENT_BINARY_DIR}
 )
 
+# GENERATE_EXPORT_HEADER doesn't do this automatically for OBJECT libraries
+TARGET_COMPILE_DEFINITIONS(lmmsobjs
+	PRIVATE -Dlmmsobjs_EXPORTS
+)
+TARGET_COMPILE_DEFINITIONS(lmms
+	PRIVATE -Dlmmsobjs_EXPORTS
+)
+
 # Set Visual Studio startup project to lmms
 # https://stackoverflow.com/a/37994396/8166701
 IF(NOT CMAKE_VERSION VERSION_LESS 3.6)