Revert removing of compile_assert.h.
Revert removing of compile_assert.h.

In https://webrtc-codereview.appspot.com/39469004 compile_assert.h is removed and that resulted in some bots to break. There is a pending CL to fix the issue https://chromereviews.googleplex.com/141837013/
, meanwhile I revert this change.

TBR=kwiberg@google.com

Review URL: https://webrtc-codereview.appspot.com/35779004

git-svn-id: 917f5d3ca488f358c4d40eaec14422cf392ccec9@8064 4adac7df-926f-26a2-2b94-8c16560cd09d

TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc