title: gdal 3.1 wants PROJ 6 symbols but my PROJ version is 7
body: <p>I'm trying to build gdal3.1 on my mac because brew only has version 2.4.4.6. I have PROJ 7.0.1 on my mac. When I run ./configure for gdal 3.1 it ends with the error: PROJ 6 symbols not found. What is needed to fix this?</p>