utils_build: cpuflags, clock_getres

After an idea in https://github.com/autotest/tp-qemu/pull/70 , I added a pull request for a builder utility:
https://github.com/autotest/virt-test/pull/1594
This is an example of how to adapt a very tricky (cpuflags) and very simple (clock_getres) TC to use utils_build. clock_getres is tested, but cpuflags is not, so see this pull request as an example until it has been tested.