toolchain: support toolchain variants

This commit enables the use of special toolchains other than
the default. Some architectures have specialized cross-compilers
within the same SDK that need to be enabled for specific platforms
of an architecture.

For example, for Intel MCUs, we have an optimized toolchain that
needs to be used for specific platforms under x86.

Change-Id: I7e25603dd66ed3ec4e019c72483c76a32b3bbdde
Signed-off-by: Anas Nashif <anas.nashif@intel.com>
2 files changed