Link error from qmakebuiltins.obj

When trying to build from the git 4.9 branch on Windows 10, with MSVC 2017_64 and Qt5.12.4 (and with jom):

qmakebuiltins.obj : error LNK2019: unresolved external symbol "class QString _cdecl QMakeInternal::qt_readRegistryKey(struct HKEY_ *,class QString const &,unsigned long)" (?qt_readRegistryKey@QMakeInternal@@YA?AVQString@@PEAUHKEY__@@AEBV2@K@Z) referenced in function "public: enum QMakeEvaluator::VisitReturn __cdecl QMakeEvaluator::evaluateBuiltinExpand(int,class ProKey const &,class ProStringList const &,class ProStringList &)" (?evaluateBuiltinExpand@QMakeEvaluator@@QEAA?AW4VisitReturn@1@HAEBVProKey@@AEBVProStringList@@AEAV4@@Z)
release\testreader.exe : fatal error LNK1120: 1 unresolved externals

here are my build steps:

mkdir build
cd build
qmake BUILD_TESTS=1 ..  (the qmake from Qt5.12.4)
jom qmake_all
jom

wild guess: QMAKE_EXPORT qt_readRegistryKey in src/shared/proparser/registry_p.h