FontConfig support built, but QT_QPA_FONTDIR still required

[danhopkins]

I'm building Qt-5.7.1 from source on Ubuntu 14.04 with FontConfig support (which appears to be detected and correctly enabled by configure)

Support enabled for:
  ...
  FontConfig ............. yes

but running apps against the build always fail with

QFontDatabase: Cannot find font directory /opt/Qt-5.7/lib/fonts.

unless overridden with an explicit QT_QPA_FONTDIR pointing at system truetype fonts. I may have misunderstood, but I assumed building FontConfig support would do this transparently. Any pointers to what I've missed or misunderstood?

Thanks