Resolve Windows conflict between zlib and angle

Windows normally defines macros so that FAR expands to far, and
far expands to nothing.

Angle undefs far, leaving the FAR macro hanging, expanding to far
which is not a legal keyword anymore. zlib already tries to handle
that someone/something has undefined FAR but it doesn't handle
that someone/something has undefined far. This patch changes that.

This problem appeared in some jumbo builds in
gpu/command_buffer/service which uses both angle and zlib.

Bug: 889429
Change-Id: Ia3b10a9a82fc51b302c67b24a19f30a73bdda489
Reviewed-on: https://chromium-review.googlesource.com/1245723
Commit-Queue: Daniel Bratell <bratell@opera.com>
Reviewed-by: Chris Blume <cblume@chromium.org>
Cr-Commit-Position: refs/heads/master@{#595425}

third_party/zlib/zconf.h

@@ -389,6 +389,9 @@
 #ifndef FAR
 #  define FAR
 #endif
+#ifndef far
+#  define far
+#endif
 
 #if !defined(__MACTYPES__)
 typedef unsigned char  Byte;  /* 8 bits */