SConstruct: fixed SConscript.generate includes
Communication: XPCC: fixed includes in unittests
SConscript: only copy enironment items if they exist
SConscript: hand parameters to unittest scons instance
SCons: PlatformTools: do not generate for hosted platform
SCons: Hosted: make clang an option for hosted

This is usefull for unittests.
Math: location 2D added template keyword requested by clang
Communication: XPCC: fixed include file paths
Driver: AD7280a: include software gpio directly in unit test

This is not a nice way of doing this but since it is only
a unit test and the only one that needs this it is ok
for the moment.
Eventually we should generate the software drivers
for a hosted platform, too.
RTOS: Boost: Mutex: include missing headerfile

This makes this file compile on Fedora 19 with
Boost 1.53 libraries.
Platform: Hosted: build if target is hosted
Driver: Disply: moved ST7036_VOLTAGE define