If there's no variant configuration, then cfg.variant will be '', which will
make bldnode be cfg.bldnode. Thus, this patch prepare gbenchmark build for
variant builds and doesn't break the current build.
We can pass a list of possible binaries to find_program. This gives us a
better output while configuring:
Checking for program 'ninja, ninja-build' : /usr/bin/ninja-build
instead of:
Checking for program 'ninja' : not found
Checking for program 'ninja-build' : /usr/bin/ninja-build
