hg: build-infra/jdk8: Since vsvars32.bat sometimes is broken, prefer the Windows SDK SetEnv.Cmd if available.

[magnus.ihse.bursie at oracle.com]

Changeset: 09e12a670446
Author:    ihse
Date:      2012-10-12 01:20 +0200
URL:       http://hg.openjdk.java.net/build-infra/jdk8/rev/09e12a670446

Since vsvars32.bat sometimes is broken, prefer the Windows SDK SetEnv.Cmd if available.

! common/autoconf/generated-configure.sh
! common/autoconf/toolchain_windows.m4