PkgConfigProbe returns raw libs output of pkg-config, which includes "-l" prefix on link library dependencies. So it can't be (easily) used with cpp.staticLibraries.

A work-around is to use cpp.linkerFlags instead. But that results in linking the libraries before the using artifacts, so they are liable to be discarded (by gcc --as-needed) causing link to fail.

I suggest PkgConfigProbe should strip the "-l" prefix so that idiomatic form becomes:

qbs.Probes.PkgConfigProbe {id: foo; name: "bar" }
cpp.cxxFlags: foo.cflags
cpp.staticLibraries: foo.libs