The idea of setting up general "toolchains" in the native build was good, but it turned out that we really only need a single toolchain, with a single twist: if it should use CC or CPP to link. This is better described by a specific argument to SetupNativeCompilation, LANG := C++ or LANG := C (the default).

There is a single exception to this rule, and that is if we want to compile for the build platform rather than the target platform. (This is only done for adlc) To keep expressing this difference, introduce TARGET_TYPE := BUILD (or TARGET_TYPE := TARGET, the default).

The final odd-case was the hack for building hsdis/bin on mingw. This can be resolved using direct variables to SetupNativeCompilation, instead of first creating a toolchain.

Doing this refactoring will simplify the SetupNativeCompilation code, and make it much clearer if we use the C or C++ linker.