On macOS 26.4, AFL builds were picking up Nix compiler-wrapper variables and Apple SDK target settings from the shell environment. That caused afl-cc to drive the wrong linker and target configuration, which broke even simple fuzz harness builds. Unset the Nix compiler and linker environment in the fuzz dev shell so AFL++ uses the system or Homebrew Apple toolchain directly. Also force afl-cc to link with lld because the newer Apple linker asserts on the custom sections emitted by AFL's LLVM instrumentation. Finally, pin fuzz-libghostty to the host target so the build does not inherit stray SDK targets from the environment.