RFR: JDK-8006661 Use LC_ALL=C instead of LANG=C in compare.sh

[Magnus Ihse Bursie]

We need to use LC_ALL=C instead of LANG=C because the latter does not 
change LC_MESSAGES, which is necessary if we are grepping for english 
words in the output from diff.

Webrev:
http://cr.openjdk.java.net/~ihse/JDK-8006661-use-LC_ALL-in-compare.sh/webrev.01
/Magnus