Qualify cmath functions.
Qualify cmath functions.

Bug: None
Change-Id: Ibfc3bbe5a21743b623ab01ae9e021d322aee2a94
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/128083
Reviewed-by: Fredrik Solenberg <a86c06127c44de4932e34935a0755af178aabab6@webrtc.org>
Commit-Queue: Mirko Bonadei <d2c43c210eae6feef04f53bae50885e8152edcca@webrtc.org>
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#27174}
ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc