Fix pkg-config call in icu test

The call had the side effect of generating extra pkg-config-wrapper.sh
in root of the build. Use different pkg-config call.

Change-Id: I8335ae55547272924802f3903ce6bba903389b62
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>

configure.pri

@@ -148,7 +148,7 @@ defineTest(qtConfTest_embedded) {
 }
 
 defineTest(qtConfTest_detectIcuuc) {
-   pkgConfig = $$first($$list($$pkgConfigExecutable()))
+   pkgConfig = $$qtConfPkgConfig()
    !isEmpty(pkgConfig) {
        qtRunLoggedCommand("$$pkgConfig --libs --static libxml-2.0", xmllibs)
        contains(xmllibs,".*-licuuc.*"):return(true)