Win64Toolchain: added 32 bit compiler configuration

It might be desirable to compile single modules with a 32 bit compiler.
Added according CMake variables so they can be used easily.

cmake/modules/MinGWCrossCompile.cmake

@@ -13,6 +13,13 @@ SET(MINGW_TOOL_PREFIX		${MINGW_PREFIX}/bin/${CMAKE_SYSTEM_PROCESSOR}-w64-mingw32
 SET(CMAKE_C_COMPILER		${MINGW_TOOL_PREFIX}gcc)
 SET(CMAKE_CXX_COMPILER		${MINGW_TOOL_PREFIX}g++)
 
+IF(WIN64)
+# specify the cross compiler
+SET(MINGW_TOOL_PREFIX32		${MINGW_PREFIX32}/bin/${CMAKE_SYSTEM_PROCESSOR32}-w64-mingw32-)
+SET(CMAKE_C_COMPILER32		${MINGW_TOOL_PREFIX32}gcc)
+SET(CMAKE_CXX_COMPILER32	${MINGW_TOOL_PREFIX32}g++)
+ENDIF()
+
 # specify location of some tools
 SET(STRIP					${MINGW_TOOL_PREFIX}strip)
 SET(WINDRES					${MINGW_TOOL_PREFIX}windres)

cmake/modules/Win64Toolchain.cmake

@@ -1,6 +1,8 @@
 SET(MINGW_PREFIX /opt/mingw64)
+SET(MINGW_PREFIX32 /opt/mingw32)
 
 SET(CMAKE_SYSTEM_PROCESSOR x86_64)
+SET(CMAKE_SYSTEM_PROCESSOR32 i686)
 
 SET(WIN64 TRUE)