prefer 'release' for non-bootstrapped host build_all configs

... like qt_tool does. otherwise we get linker errors with debug builds
on windows.

Change-Id: I583f277ff3fb75c9fe5f305a6f1b5d066b840c07
Reviewed-by: Debao Zhang <hello@debao.me>
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>
Reviewed-by: Jonathan Liu <net147@gmail.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>

mkspecs/features/qt_module.prf

@@ -35,6 +35,8 @@ host_build {
             QT -= core core-private xml
             QT += bootstrap-private
         }
+    } else {
+        !build_pass:contains(QT_CONFIG, build_all): CONFIG += release
     }
 }