'cibuildme' , when placed in a commit log, will force
a distcheck build on CI if no build files have changed
also includes:
ci: move distcheck build skipping to earliest possible place in build
this breaks out the script to evaluate whether a distcheck should occur
into a separate file and runs it in the before_install hook, setting
a variable on skip
running configure or any commands at all is unnecessary if the distcheck
build will be skipped, so just update the last-distcheck file and abort
the build immediately to save time
ref D6735