src/poky:gcc-target: Ensure buildtools-extended-tarball doesn't use a…

…rch=native

A nativesdk BBCLASSEXTEND was added to gcc-target without realising this
would pass arch=native through to it for x86-64. This heavily optimises
gcc output for the host its running on meaning it can't be reused via
sstate on other machines.

Add class-target overrides here to get the desired behaviour. All
targets have been covered for completeness.

(From OE-Core rev: d0d4853dd773f7bbe0f72e50144559b80e80d67a)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>