Can't get qmake to work from command line on MacOS High Sierra

[lordnoriyuki]

MacOS High Sierra 10.13
QT 5.9.2 or QT 5.10.0 beta

Installed QT in ~/Qt

I can build just fine from QtCreator, but if I try to use qmake from the command line I always get (for any project I try):

Project ERROR: failed to parse default search paths from compiler output

For example, from the basiclayouts example:

/Users/###/Qt/5.10.0/clang_64/bin/qmake -o Makefile ../basiclayouts/basiclayouts.pro -spec macx-clang CONFIG+=debug CONFIG+=x86_64 CONFIG+=qml_debug
Project ERROR: failed to parse default search paths from compiler output

With debug on qmake, it looks like this is the point where it fails:

DEBUG 1: /Users/###/Qt/5.10.0/clang_64/mkspecs/features/toolchain.prf:142: calling built-in isEmpty(QMAKE_DEFAULT_LIBDIRS)

So QMAKE_DEFAULT_LIBDIRS is empty but isn't expected to be.

Clang version details:

Apple LLVM version 9.0.0 (clang-900.0.37)
Target: x86_64-apple-darwin17.0.0

Any ideas what I've got set up wrong?

Thanks