lib/oe/utils.py: add get_host_compiler_version()

Add helper function to get the host compiler and version.
Do not assume compiler is gcc.

NOTE: cannot set env to d.getVar("PATH") as that does not contain
the session PATH which was set by environment-setup-... which
breaks the install-buildtools use-case

Signed-off-by: Tim Orling <timothy.t.orling@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>