Add recipe-sysroot path to the standalone test build

Module dependency lookup mechanism requires all Qt dependencies
acessible through the paths specified in PATHS parameter of the
find_dependency call. Since cross-repo dependencies are available
only in recipe-sysroot, it's necessary to add it explicitly
to the QT_ADDITIONAL_PACKAGES_PREFIX_PATH cache variable.

Change-Id: I506456bc715943ae7ba2ebe61e1a38936bb93a31
Reviewed-by: Samuli Piippo <samuli.piippo@qt.io>

recipes-qt/qt6/qt6-ptest.inc

@@ -21,7 +21,7 @@ fakeroot do_install_ptest() {
             -DCMAKE_TOOLCHAIN_FILE=${WORKDIR}/toolchain.cmake \
             ${EXTRA_OECMAKE} \
             -DQT_BUILD_STANDALONE_TESTS=ON \
-            -DQT_ADDITIONAL_PACKAGES_PREFIX_PATH=${D}${QT6_INSTALL_LIBDIR}/cmake \
+            -DQT_ADDITIONAL_PACKAGES_PREFIX_PATH="${D}${QT6_INSTALL_LIBDIR}/cmake;${RECIPE_SYSROOT}/${QT6_INSTALL_LIBDIR}/cmake" \
             -DCMAKE_STAGING_PREFIX=${D}${prefix} \
             ${S} \
             -Wno-dev