Fix an accidental bug introducted by the pthreads changes. When creating
a resume thread the handler function was accidentally changed from
ztest_resume to ztest_resume_thread. There's a decent chance this
may explain some/all of the crashes that have be observed running
ztest. This issue was exposed and easily fixed once the -Wno-unused
check was removed from the build system. Happily at least one real
bug fix resulted from that cleanup.
9de6723b83