[compiler-rt] [nsan] More unit tests for `float128`. (PR #165248)

[Marco Elver via llvm-commits]

melver wrote:

I'm seeing
```
  /home/gha/actions-runner/_work/llvm-project/llvm-project/compiler-rt/lib/nsan/tests/NSanUnitTest.cpp:60:47: error: use of undeclared identifier 'nextafterf128'
     60 | TEST(NSanTest, Float128) { TestFT<__float128, nextafterf128>(); }
        |                                               ^~~~~~~~~~~~~
  1 error generated.
```
Can you revert or fix-forward?
Thanks!

https://github.com/llvm/llvm-project/pull/165248