[libcxx-commits] [libcxx] [libc++] Conditionally declare `lgamma_r` as noexcept (PR #156547)

[Nico Weber via libcxx-commits]

nico wrote:

We're also getting build errors on fuchsia with this:

```
[282/101447] CXX obj/third_party/abseil-cpp/absl/strings/cordz_functions/cordz_functions.o
../../third_party/llvm-build/Release+Asserts/bin/clang++ -MMD -MF obj/third_party/abseil-cpp/absl/strings/cordz_functions/cordz_functions.o.d ...(too long)
In file included from ../../third_party/abseil-cpp/absl/strings/internal/cordz_functions.cc:20:
In file included from ../../third_party/libc++/src/include/random:1685:
../../third_party/libc++/src/include/__random/binomial_distribution.h:114:19: error: exception specification in declaration does not match previous declaration
  114 | extern "C" double lgamma_r(double, int*) _LIBCPP_LGAMMA_R_NOEXCEPT;
      |                   ^
../../third_party/fuchsia-sdk/sdk/obj/x64-api-28/sysroot/include/math.h:398:8: note: previous declaration is here
  398 | double lgamma_r(double, int*);
      |        ^
1 error generated.
```

https://github.com/llvm/llvm-project/pull/156547