hg: jdk8u/jdk8u-dev/langtools: 8220495: Update GIFlib library to the 5.1.8

[dcherepanov at azul.com]

Changeset: 585c9a1ce7eb
Author:    serb
Date:      2019-03-31 16:57 -0700
URL:       http://hg.openjdk.java.net/jdk8u/jdk8u-dev/langtools/rev/585c9a1ce7eb

8220495: Update GIFlib library to the 5.1.8
Reviewed-by: prr

! THIRD_PARTY_README