Roll openh264 to 2e96d62 and fix symbols getting improperly exported

This is needed to pick up the symbol visibility changes introduced by [1].  This
CL also sets symbols to hidden for non-component builds on Linux and Mac.

[1] https://github.com/cisco/openh264/commit/9e056ba16eb9d374347495ea33e94d959f0cf54a

R=jochen

Change-Id: I158f33866ffa1256eabf05b277ce0dfa98bb9121
Bug: None
Reviewed-on: https://chromium-review.googlesource.com/864841
Reviewed-by: Jochen Eisinger <[email protected]>
Commit-Queue: Thomas Anderson <[email protected]>
Cr-Commit-Position: refs/heads/master@{#529343}
4 files changed