[libc] Implement sincosf function correctly rounded to all rounding modes.

Refactor common range reductions and evaluations for sinf, cosf, and
sincosf.  Added exhaustive tests for sincosf.

Performance before the patch:
```
System LIBC reciprocal throughput : 30.205
LIBC reciprocal throughput        : 30.533

System LIBC latency : 67.961
LIBC latency        : 61.564
```
Performance after the patch:
```
System LIBC reciprocal throughput : 30.409
LIBC reciprocal throughput        : 20.273

System LIBC latency : 67.527
LIBC latency        : 61.959
```

Reviewed By: orex

Differential Revision: https://reviews.llvm.org/D130901