This is a follow-up to #157517, which fixes the remaining math/smoke
tests, and changes them to only include `hdr/errno_macros.h`, as the
tests just need the errno values to pass into `EXPECT_MATH_ERRO` macro.
A couple non-mechanical changes include:

* slightly better test coverage for some exp/log tests -- that actually
validates that errno is set to `EDOM` or `ERANGE` for certain inputs;
* explicit inclusion of `src/__support/libc_errno.h` in
RoundToIntegerTest template, which still needs to be fixed.

With this change there's a single libc_errno usage left:
```
$ grep -lrnH "libc_errno.h" test/src/math/smoke
test/src/math/smoke/RoundToIntegerTest.h
```

This is the first step in preparation for:
https://discourse.llvm.org/t/rfc-make-clang-builtin-math-functions-constexpr-with-llvm-libc-to-support-c-23-constexpr-math-functions/86450

Add tests for signaling NaNs, and fix function behavior for handling
signaling NaN input.

Fixes https://github.com/llvm/llvm-project/issues/124812

Fixes https://github.com/llvm/llvm-project/issues/124801.

Half-precision floating point (16-bit) implementation of the
trigonometric function Sin for inputs scaled by pi