Main function in quadopt.cc can be useful

[jamesgk]

I'm wondering, was there any particular reason the main function in quadopt.cc was removed in 9cdf21d9afb52ce9a89e6a71698bdbeae0eb6531? Just because it was unused in this module? In that case, I'd recommend putting it back since quadopt.cc can be useful on its own (see https://github.com/google/roboto/blob/master/third_party/fontcrunch/Makefile).