configure: make config.status work for in-source builds on unix

Change-Id: Ib2a62e71a88f46836c10b0d9c47da5ad1f98d413
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@qt.io>

configure.pri

@@ -1303,6 +1303,7 @@ defineTest(createConfigStatus) {
         cont = \
             "$$system_quote($$system_path($$cfg)$$ext) -redo %*"
     } else {
+        !contains(cfg, .*/.*): cfg = ./$$cfg
         cont = \
             "$${LITERAL_HASH}!/bin/sh" \
             "exec $$system_quote($$cfg) -redo \"$@\""