No longer builds on Arch/Manjaro

When trying to build I get this error:

cd lib/ && ( test -e Makefile.shared || /usr/sbin/qmake-qt5 -o Makefile.shared /build/src/libarchive-qt-v1.0.2/lib/shared.pro ) && /usr/sbin/make -f Makefile.shared install
make[1]: Entering directory '/build/src/libarchive-qt-v1.0.2/lib'
/usr/sbin/qmake-qt5 -install qinstall -exe libarchiveqt5.so.1.1.0 /build/pkg/libarchive-qt/usr/lib/libarchiveqt5.so.1.1.0
/usr/sbin/qmake-qt5 -install qinstall /build/src/libarchive-qt-v1.0.2/lib/libarchiveqt.h /build/pkg/libarchive-qt/usr/include/libarchiveqt.h
/usr/sbin/qmake-qt5 -install qinstall /build/src/libarchive-qt-v1.0.2/lib/ChangeLog /build/pkg/libarchive-qt/usr/share/libarchiveqt5/ChangeLog
strip --strip-unneeded /build/pkg/libarchive-qt/usr/lib/libarchiveqt5.so.1.1.0
/usr/sbin/qmake-qt5 -install qinstall /build/src/libarchive-qt-v1.0.2/lib/README /build/pkg/libarchive-qt/usr/share/libarchiveqt5/README
ln -f -s libarchiveqt5.so.1.1.0 /build/pkg/libarchive-qt/usr/lib/libarchiveqt5.so
ln -f -s libarchiveqt5.so.1.1.0 /build/pkg/libarchive-qt/usr/lib/libarchiveqt5.so.1
ln -f -s libarchiveqt5.so.1.1.0 /build/pkg/libarchive-qt/usr/lib/libarchiveqt5.so.1.1
install -m 644 -p pkgconfig/archiveqt5.pc /build/pkg/libarchive-qt/usr/lib/pkgconfig/archiveqt5.pc
/usr/sbin/install: cannot stat 'pkgconfig/archiveqt5.pc': No such file or directory
make[1]: *** [Makefile.shared:455: install_target] Error 1
make[1]: Leaving directory '/build/src/libarchive-qt-v1.0.2/lib'
make: *** [Makefile:61: sub-lib-shared-pro-install_subtargets] Error 2
==> ERROR: A failure occurred in package().

The command in the PKGBUILD is: make INSTALL_ROOT=${pkgdir} install

So it's something in the Makefile of the project.

PS: Arch (and Manjaro) uses pkgconf now, which provides pkg-config.