gitlab-ci: Fix the ARMv7 triple
Previously we were configuring the ARMv7 builds with a host/target
triple of arm-linux-gnueabihf, which caused us to target ARMv6 and
consequently rely on the old CP15 memory barrier implementation. This
barrier has to be emulated on ARMv8 machines which is glacially slow.
Hopefully this should fix the ARMv7 builds which currently consistently