[non-BE] [split-non-BE] Fix non-BE between optimization levels in dft stereo for Apple Clang

• Related issues: #1397
• Requested reviewers: @fotopoulou @tyagiri

Reason why this change is needed

• Achieve BE between compiler optimization levels for easier conformance testing

Description of the change

• replace sinf and cosf with BASOP implementation in DFT stereo encoder

Affected operating points

• All DFT-Stereo core coder modes
• bitstream and output are changed, but no interop problems

Related to #1397