Exclude protoc objects from merge_libs.py.
Exclude protoc objects from merge_libs.py.

BUG=b/12567343
R=wjia@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/7249004

Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 8f35afab8cd4a860d3fc6962fd87e440f39e7245

sippet/webrtc,sippet/webrtc,sippet/webrtc,sippet/webrtc,sippet/webrtc,sippet/webrtc