Various configure and build enhancements:
- Auto detect availability of wxWidgets, disable or enable examples build accordingly
- Enhacend (cross) toolchain detection and prefix. Now compile win32 target on linux host (--cc=i686-mingw32-gcc)

Authors :
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Edouard TISSERANT (www.lolitech.fr)
Francis DUPIN (LIVIC)
Laurent BESSARD (www.lolitech.fr)