MSVC: Fix plugins not loading with debug builds

The "d" suffix used in debug builds breaks plugin loading because LMMS
expects to find a descriptor named e.g. "kickerd_plugin_descriptor" instead
of "kicker_plugin_descriptor" when discovering a plugin with the filename
"kickerd.dll".

plugins/CMakeLists.txt

@@ -1,5 +1,6 @@
 SET(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR})
 SET(CMAKE_LIBRARY_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR})
+SET(CMAKE_DEBUG_POSTFIX "")
 
 # Enable C++11
 SET(CMAKE_CXX_STANDARD 11)