ocamlPackages.dtoa: disable hardening feature based on more accurate condition
ocamlPackages.dtoa: disable hardening feature based on more accurate condition

The `strictoverflow` hardening feature causes a build failure when using Clang as the compiler, not just on Darwin.

NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs