Add pkg-config files and makefiles

BUG=chromium:710465
TEST=emerge webrtc-apm on eve and veyron
to verify libwebrtc_apm.so is built and
libwebrtc_apm.pc is installed

Change-Id: Ic05e3ee48ca8e4de5c9e06b78ca46defe8a232fd
Reviewed-on: https://chromium-review.googlesource.com/970199
Commit-Ready: Hsinyu Chao <hychao@chromium.org>
Tested-by: Hsinyu Chao <hychao@chromium.org>
Reviewed-by: Cheng-Yi Chiang <cychiang@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
39 files changed