make linkerSupportsFlag() use gold linker if detected

subsequent tests should depend on the detected linker, obviously.

Change-Id: I09aa9f1f2ef789f0ae0829f9122211fc4e1ad518
Reviewed-by: Joerg Bornemann <joerg.bornemann@theqtcompany.com>

configure

@@ -376,6 +376,9 @@ linkerSupportsFlag()
 	safe_flag=`shellEscape "$flag"`
 	lflags=$lflags,$safe_flag
     done
+    if [ $CFG_USE_GOLD_LINKER = yes ]; then
+        lflags="-fuse-ld=gold $lflags"
+    fi
     compilerSupportsFlag $compiler $lflags
 }