libgd: disable fontconfig on OSX

[vbraun]

Neither OSX nor Sage ship with fontconfig, but it is sometimes picked up from third-party distributions (leading to compile failures). Disable on OSX by default.

Note that upstream changed from "gd" to "libgd", we should probably update (but on another ticket).

Component: build

Author: Volker Braun

Branch/Commit: u/vbraun/libgd__disable_fontconfig_on_osx @ f5e0f74

Reviewer: Sami Losoi

Issue created by migration from https://trac.sagemath.org/ticket/15736

[vbraun]

Author: Volker Braun

[vbraun]

Branch: u/vbraun/libgd__disable_fontconfig_on_osx

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

f5e0f74

remove incorrect quotes

[sagetrac-git]

Commit: f5e0f74

[sagetrac-slosoi]

comment:6

The building was this time success with the proposed change.

Please, see the log which came to the terminal with many warnings, however not relevant to this ticket:
https://dl.dropboxusercontent.com/u/62073194/install_terminal.log
I think these warnings are coming from bad practices used in third-party packages.

Please, see the autogenerated log which confirms that there were no errors in building Sage with the change proposed by Volker Braun:
https://dl.dropboxusercontent.com/u/62073194/install2.log

[vbraun]

Reviewer: Sami Losoi