Installing Postgresql parray_gin extension on mac, include not found

I am trying to install parray_gin in PostgreSQL 10 on macOS, but I can't get it to build. I'm running pgxn install parray_gin. This first gave me a missing stdio.h error, so I installed the xcode command line tools, and now it's complaining about /Library/PostgreSQL/10/include/postgresql/server/utils/pg_locale.h:19:10: fatal error: 'unicode/ucol.h' file not found After some Googling it appeared I needed to install an extra library, which I did through brew install icu4c This printed: This formula is keg-only, which means it was not symlinked into /usr/local, because macOS provides libicucore.dylib (but nothing else). If you need to have this software first in your PATH run: echo 'export PATH="/usr/local/opt/icu4c/bin:$PATH"' >> ~/.bash_profile echo 'export PATH="/usr/local/opt/icu4c/sbin:$PATH"' >> ~/.bash_profile For compilers to find this software you may need to set: LDFLAGS: -L/usr/local/opt/icu4c/lib CPPFLAGS: -I/usr/local/opt/icu4c/include But it didn't change a thing and I have no idea how to pass /usr/local/opt/icu4c/include to pgxn