Fix library inclusion order when building statically

When building application statically, it's important to keep libraries
we're linking against in order. qmake's "*=" operator fails to do that,
so use "+=" instead.

Change-Id: Id3627da47d07c70fd07185a777f2f07bb4057f03
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>

config.tests/unix/compile.test

@@ -67,7 +67,7 @@ test -r Makefile && $MAKE distclean >/dev/null 2>&1
 # Make sure output from possible previous tests is gone
 rm -f "$EXE" "${EXE}.exe"
 
-set -- "$OUTDIR/bin/qmake" -nocache -spec "$QMKSPEC" "CONFIG+=$QMAKE_CONFIG" "CONFIG+=android_app" "CONFIG-=debug_and_release app_bundle lib_bundle" "LIBS*=$LFLAGS" "LIBS+=$MAC_ARCH_LFLAGS" "INCLUDEPATH*=$INCLUDEPATH" "QMAKE_CXXFLAGS*=$CXXFLAGS" "QMAKE_CXXFLAGS+=$MAC_ARCH_CXXFLAGS" "$SRCDIR/$TEST/$EXE.pro" -o "$OUTDIR/$TEST/Makefile"
+set -- "$OUTDIR/bin/qmake" -nocache -spec "$QMKSPEC" "CONFIG+=$QMAKE_CONFIG" "CONFIG+=android_app" "CONFIG-=debug_and_release app_bundle lib_bundle" "LIBS+=$LFLAGS" "LIBS+=$MAC_ARCH_LFLAGS" "INCLUDEPATH*=$INCLUDEPATH" "QMAKE_CXXFLAGS*=$CXXFLAGS" "QMAKE_CXXFLAGS+=$MAC_ARCH_CXXFLAGS" "$SRCDIR/$TEST/$EXE.pro" -o "$OUTDIR/$TEST/Makefile"
 if [ "$VERBOSE" = "yes" ]; then
     OUTDIR=$OUTDIR "$@" && $MAKE && SUCCESS=yes
 else