The CI is using ubuntu artful and the deb package is compiled with another
compiler that gcc-4.8 (used in other project CI).
As we compile everything with gcc-4.8, we must compile our own ctpp2.
Introduce also a "NeutralEnv", a build environment independent of the
targeted platform. All `Source` now build using the neutralEnv.
Most of toolchains are also using neutralEnv except android_ndk who is
specific to a platform.
As toolchain are neutral, platform specific environment variables are now
set by the platformInfo directly instead of the toolchain.
Matthieu Gautier