USES_GCC: is "yes:build+" valid?

I'm working on updating sysutils/uefi-edk2-bhyve and ran portlint.

It's complaining about the "USE_GCC:yes:build" line, saying:


WARN: Makefile: [22]: Setting a specific version for USE_GCC should only 
be done as a last resort.  Unless you have confirmed this port does not 
build with later versions of GCC, please use USE_GCC=yes:build+.

I didn't see any documentation for "yes:build+" online, so I was 
wondering if that's really valid?


-- 

Rebecca Cran