Map current TARGET_ARCH to the ABI used by qtcreator. Currently mapping
was done by kernel-arch.bbclass and it worked by accident, but it's now
broken in jethro.

Change-Id: I15c5b60a1bc1dd560685fedac9b61048a1e89266
Reviewed-by: Risto Avila <risto.avila@theqtcompany.com>
Reviewed-by: Teemu Holappa <teemu.holappa@theqtcompany.com>