CMakeLists.txt: install libFLAC-8.dll for win32 build

After updating some external libraries, libFLAC-8.dll is now required
as well, so install it into the win32 package.

CMakeLists.txt

@@ -449,6 +449,7 @@ IF(LMMS_BUILD_WIN32)
 					${MINGW_PREFIX}/bin/libogg-0.dll
 					${MINGW_PREFIX}/bin/libfluidsynth-1.dll
 					${MINGW_PREFIX}/bin/libfftw3f-3.dll
+					${MINGW_PREFIX}/bin/libFLAC-8.dll
 					${MINGW_PREFIX}/bin/SDL.dll
 					${MINGW_PREFIX}/bin/libglib-2.0-0.dll
 					${MINGW_PREFIX}/bin/libgthread-2.0-0.dll