<AWT Dev> [13] Review Request: 8220495 Update GIFlib library to the latest 5.1.8

[Sergey Bylokhov]

Hello.
Please review the fix for JDK 13.

Bug: https://bugs.openjdk.java.net/browse/JDK-8220495
Fix: http://cr.openjdk.java.net/~serb/8220495/webrev.02

The giflib was updated from 5.1.4 to 5.1.8.

The is mostly a replacement of old files(5.1.4) by the new files(5.1.8) except two additional steps.
  - The library uses "<unistd.h>" which breaks the build on windows, and "<stdbool.h>" wihch does not work properly on old Solaris.
    It was fixed by this patch(same as in 5.1.4 during previous upgrade):
    http://cr.openjdk.java.net/~serb/8220495/giflib

  - I have drop the usage of "tabs" and manually reformat the code to make the diff smaller.

Mach5 on all platforms is green.

-- 
Best regards, Sergey.