[8] RFA 8203845: backport of JDK-8034788 inadvertently rolled back JDK-8187045 changes to toolchain.m4

[David Buck]

Hi!

Please approve the push of this simple regression fix to 8u-dev. As this 
is an issue in only JDK 8, there is no fix needed for later versions.

bug report:
https://bugs.openjdk.java.net/browse/JDK-8203845

webrev:
http://cr.openjdk.java.net/~dbuck/8203845.0/

code review:
http://mail.openjdk.java.net/pipermail/build-dev/2018-May/022223.html

JPRT hostspot tests passed and manual confirmation of fix done.

Cheers,
-Buck