qt5base-lts/mkspecs/features/qmake_use.prf

suffix =
for(ever) {
    CC_USES =
    LD_USES =
    for (use, QMAKE_USE$${suffix}) {
        use = $$split(use, /)
        name = $$take_first(use)
        nu = $$upper($$replace(name, -, _))
        !contains(use, linkonly): CC_USES += $$nu
        !contains(use, nolink): LD_USES += $$nu
    }
    CC_USES = $$resolve_depends(CC_USES, QMAKE_DEPENDS_, _CC)
    for (nu, CC_USES) {
        !defined(QMAKE_LIBS_$$nu, var): \
            error("Library '$$lower($$replace(nu, _, -))' is not defined.")

        DEFINES += $$eval(QMAKE_DEFINES_$${nu})
        INCLUDEPATH += $$eval(QMAKE_INCDIR_$${nu})
    }
    LD_USES = $$resolve_depends(LD_USES, QMAKE_DEPENDS_, _LD)
    for (nu, LD_USES) {
        !defined(QMAKE_LIBS_$$nu, var): \
            error("Library '$$lower($$replace(nu, _, -))' is not defined.")

        debug: \
            LIBS$${suffix} += $$eval(QMAKE_LIBS_$${nu}_DEBUG) $$eval(QMAKE_LIBS_$$nu)
        else: \
            LIBS$${suffix} += $$eval(QMAKE_LIBS_$${nu}_RELEASE) $$eval(QMAKE_LIBS_$$nu)
    }
    !isEmpty(suffix): break()
    suffix = "_PRIVATE"
}