[8u] RFR: Backport 8216354: Syntax error in toolchain_windows.m4

[Simon Tooke]

This is a request to backport the changes required to fix 8216354.  It's
been sitting on my TODO pile for too long.

The actual 8216354 was fixed as part of a later commit, but I have
webrevs to just backport the relevant change (one line) to jdk8u and
11u.  I'll be sending out this identical RFR on both lists as separate
threads.

Bug: https://bugs.openjdk.java.net/browse/JDK-8216354

Webrev (jdk8u): http://cr.openjdk.java.net/~stooke/webrevs/jdk-8216354-jdk8/

Webrev (jdk11u):
http://cr.openjdk.java.net/~stooke/webrevs/jdk-8216354-jdk11/

Thank you for your time,

-Simon.