build system: Fixed CCACHE/DISTCC/SYSROOT space issues

build system: Fixed CCACHE/DISTCC/SYSROOT space issues
- The preprocessor must be passed to ecp/ecc with -cpp "$(CPP)"
- The definitions of CC/CPP/CXX must not contain any spaces
- CCACHE_COMPILE/DISTCC_COMPILE must contain their own extra space at the end if set, with $(space), otherwise must be empty string