The toolchain_* files are target OS specific so they were moved to
the target OS subdir.
The gcc_version.* files are only cleared once per make instantiation so
a build that creates multiple HW targets will try to link with an
incompatible .o file (i.e. x86 build linking ARM .o). I created
posix-arm as a separate target to fix this problem.
Signed-off-by: Mark Charlebois <charlebm@gmail.com>
