Update TOOLCHAIN_OUTPUTNAME to rename the output package which is the
similiar style to name packages meta-toolchain-*.
[YOCTO #3996]
(From OE-Core rev: e40c36ff8610ebb9ce16a4d1c14c7cf94f87cd6a)
Signed-off-by: Kang Kai <kai.kang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>