JDK 14 RFR: 8216354: Syntax error in toolchain_windows.m4

[Simon Tooke]

This is a trivial fix that has been sitting around since JDK8. 

At one time, 8216354 was marked "won't fix", but I've seen people
(including myself) run up against this issue enough that I think it
should be addressed.  It's been reopened, and I have a webrev ready that
I've tested in the jdk repo, on Windows.  It fixes the issue as
described in the bug description.  I have tested the patch using a
Cygwin build but not a WSL build.

This patch alters a change introduced in
https://hg.openjdk.java.net/jdk/jdk/annotate/50677f43ac3d/make/autoconf/toolchain_windows.m4#l746
That change introduced an issue that prevented the use of directories
with spaces.

If this patch is accepted, I intend to backport it to 11u and 8u.

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

Webrev: http://cr.openjdk.java.net/~stooke/webrevs/jdk-8216354-jdk14/00/

Thank you,

-Simon