Explicit declare gbm library directory

Explicit declare gbm library directory

We are checking gbm system library and cflags using pkg, therefore its
directory ought to be checked in the same way.

I spotted this problem in a Ubuntu 12.04 system where my custom pkg directory
is rather clean, without superfluous libraries. Probably no other developer
noticed this bug before because in the working pkg directory was already being
pulled in by libgestures or any other configuration that uses --libs-only-L
in system.gyp.

BUG=none
TEST=embedded=1 ozone_platform_gbm=1, linking content_shell

Committed: https://crrev.com/5cdbf79d872e2bbdcf8994da76ef156bc9bacbbc
Cr-Commit-Position: refs/heads/master@{#293903}

[vignatti (out of this project), 2014-09-08 07:48:35]

tiago.vignatti@intel.com changed reviewers:
+ brettw@chromium.org, dnicoara@chromium.org, spang@chromium.org

[vignatti (out of this project), 2014-09-08 07:48:59]

brettw@ PTAL.

[dnicoara, 2014-09-08 13:34:24]

lgtm

[brettw, 2014-09-08 20:08:15]

lgtm

[vignatti (out of this project), 2014-09-09 07:40:38]

The CQ bit was checked by tiago.vignatti@intel.com

[commit-bot: I haz the power, 2014-09-09 07:41:26]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/tiago.vignatti@intel.com/553793002/1

[commit-bot: I haz the power, 2014-09-09 09:19:07]

Committed patchset #1 (id:1) as 77daf708e63e8b2d5e39ba80e794ea98af5e879c

[commit-bot: I haz the power, 2014-09-10 03:52:14]

Patchset 1 (id:??) landed as
https://crrev.com/5cdbf79d872e2bbdcf8994da76ef156bc9bacbbc
Cr-Commit-Position: refs/heads/master@{#293903}