Fixed nix build for macos.

[diasbruno]

I'm not an expert on nix, so I'd appreciate some help with this.

On macOS, the nix was failing because it was finding the llvm 16 on the nix hash.

I updated the flake, and added the missing piece "compiler-rt" to find the rest of the runtime libraries.

This hash pushes llvm to version 19.

[diasbruno]

I tested on a Ubuntu x86_64 on WSL and it compiled and run ok.

[lerno]

This one looks wrong. You'd adding the configurable path yes, but you don't default to the LLVM one, so any build outside of nix breaks.

[diasbruno]

You are right. I forgot to build with the local llvm. 🤦‍♂️

[lerno]

Wouldn't it make more sense to make the override to change from the default if the override is set to a value, rather than have it depend on nix?

So "if LLVM_CRT_LIBRARY_DIR is empty string, use the default, otherwise use the code with LLVM_CRT_LIBRARY_DIR"

[diasbruno]

This seems to be Apple only so I decided to only set on this if. But I'm ok setting as default.

[lerno]

I meant to get rid of the C3_IS_NIX_BUILD entirely and only use LLVM_CRT_LIBRARY_DIR if it is set to a non-empty value.

[lerno]

Hmm.. that failed

[lerno]

Maybe this is better:

option(LLVM_CRT_LIBRARY_DIR "Use custom llvm's compiler-rt directory" "")
...
find_file(RT_ASAN_DYNAMIC NAMES libclang_rt.asan_osx_dynamic.dylib PATHS ${LLVM_CRT_LIBRARY_DIR} "${LLVM_LIBRARY_DIR}/clang/${LLVM_MAJOR_VERSION}/lib/darwin")
find_file(RT_TSAN_DYNAMIC NAMES libclang_rt.tsan_osx_dynamic.dylib PATHS ${LLVM_CRT_LIBRARY_DIR} "${LLVM_LIBRARY_DIR}/clang/${LLVM_MAJOR_VERSION}/lib/darwin")
find_file(RT_UBSAN_DYNAMIC NAMES libclang_rt.ubsan_osx_dynamic.dylib PATHS ${LLVM_CRT_LIBRARY_DIR} "${LLVM_LIBRARY_DIR}/clang/${LLVM_MAJOR_VERSION}/lib/darwin")
find_file(RT_LSAN_DYNAMIC NAMES libclang_rt.lsan_osx_dynamic.dylib PATHS ${LLVM_CRT_LIBRARY_DIR} "${LLVM_LIBRARY_DIR}/clang/${LLVM_MAJOR_VERSION}/lib/darwin")