build fails on macOS

[Ben Abbott]

jwe,

On macOS and using Homebrew for dependencies, the build process broke for me 
after the changes below.

http://hg.savannah.gnu.org/hgweb/octave/rev/332be8be16eb
http://hg.savannah.gnu.org/hgweb/octave/rev/4b661d535ddb

The error I see is below. Which looks to indicates a variable got dropped or 
“-framework” was added somewhere by mistake.

        No rule to make target `-framework', needed by 
`libgui/graphics/__init_qt__.la’

I’m happy to help debug. But need some guidance.

Ben