qbs files: Fix compilation for cpp.linkerFlags updated

Change-Id: I8d5b9136d349104b3c6d81ad11d120a9afdf3f70
Reviewed-by: Joerg Bornemann <joerg.bornemann@nokia.com>

src/libs/3rdparty/botan/botan.qbs

@@ -62,7 +62,7 @@ QtcLibrary {
         Depends { name: "cpp" }
         cpp.linkerFlags: {
             if (qbs.toolchain == "mingw") {
-                return ["--enable-auto-import"]
+                return ["-Wl,--enable-auto-import"]
             }
         }
         cpp.includePaths: '..'