unbreak tst_qresourceengine for prefix builds

don't try to execute a binary from the install dir.

amends 8e776d3.

Change-Id: I37990bc83b295379f0c93f4ca712e1bbf980fd44
Reviewed-by: Oliver Wolff <oliver.wolff@qt.io>

tests/auto/corelib/io/qresourceengine/qresourceengine.pro

@@ -5,9 +5,10 @@ QT = core testlib
 SOURCES = tst_qresourceengine.cpp
 RESOURCES += testqrc/test.qrc
 
+qtPrepareTool(QMAKE_RCC, rcc, _DEP)
 runtime_resource.target = runtime_resource.rcc
-runtime_resource.depends = $$PWD/testqrc/test.qrc
-runtime_resource.commands = $$[QT_INSTALL_BINS]/rcc -root /runtime_resource/ -binary $${runtime_resource.depends} -o $${runtime_resource.target}
+runtime_resource.depends = $$PWD/testqrc/test.qrc $$QMAKE_RCC_EXE
+runtime_resource.commands = $$QMAKE_RCC -root /runtime_resource/ -binary $$PWD/testqrc/test.qrc -o $${runtime_resource.target}
 QMAKE_EXTRA_TARGETS = runtime_resource
 PRE_TARGETDEPS += $${runtime_resource.target}
 QMAKE_DISTCLEAN += $${runtime_resource.target}