RFR: JDK-8218413 make reconfigure ignores configure-time AUTOCONF environment variable

Mon Feb 11 11:42:55 UTC 2019

 From the bug report:

"Suppose PATH points to an out-of date autoconf.
We can use the AUTOCONF environment variable with configure to override 
finding autoconf on PATH, but that variable is not remembered, so
make reconfigure fails.

# Recipe:
rm -rf build
AUTOCONF=/usr/bin/autoconf PATH="$MOLDY/bin:$PATH" bash configure ...
# configure + make succeed

make reconfigure
# Fails with:
Using autoconf at $MOLDY/bin/autoconf [autoconf (GNU Autoconf) 2.62]
stdin:33: error: Autoconf version 2.69 or higher is required"

Bug: https://bugs.openjdk.java.net/browse/JDK-8218413
WebRev: 
http://cr.openjdk.java.net/~ihse/JDK-8218413-preserve-AUTOCONF-for-reconfigure/webrev.01

/Magnus