Fix bench to compile when SK_SUPPORTS_GPU is not provided as a compiler option

Fix bench to compile when SK_SUPPORTS_GPU is not provided as a compiler option

In the case that SK_SUPPORTS_GPU is not provided to the compiler, the value is
either defined in in the SkUserConfig.h or SkPostConfig.h. Prior to this change
HairlinePathBench would test that value before including anything, which led to
build errors.

BUG=skia:

Committed: http://code.google.com/p/skia/source/detail?r=13502

[bsalomon, 2014-02-19 19:16:56]

lgtm

[commit-bot: I haz the power, 2014-02-19 19:17:02]

CQ is trying da patch. Follow status at
https://skia-tree-status.appspot.com/cq/cdalton@nvidia.com/172103007/1

[commit-bot: I haz the power, 2014-02-19 19:30:43]

Change committed as 13502