Can't pass LDFLAGS or CFLAGS to runtime bindings

[theoparis]

I have a custom xcode toolchain on my macOS machine, and It requires linking directly against libcxxabi.a and libcxx.a for some reason (otherwise it tries to use the dynamically linked version which needs patching with install_name_tool due to it using rpaths). I tried
RUSTFLAGS="-Clink-arg=-fuse-ld=lld -Clink-arg=/Library/Developer/Toolchains/LLVM20.0.0git.xctoolchain/usr/lib/libc++.a -Clink-arg=/Library/Developer/Toolchains/LLVM20.0.0git.xctoolchain/usr/lib/libc++abi.a" LDFLAGS="-fuse-ld=lld /Library/Developer/Toolchains/LLVM20.0.0git.xctoolchain/usr/lib/libc++.a /Library/Developer/Toolchains/LLVM20.0.0git.xctoolchain/usr/lib/libc++.a /Library/Developer/Toolchains/LLVM20.0.0git.xctoolchain/usr/lib/libc++abi.a cargo install --path helix-term
And it seems like the LDFLAGS variable doesn't get passed to each runtime binding's build.rs:

 dyld[86159]: Symbol not found: ___cxa_demangle
    Referenced from: <FDE9B676-8FF7-3D2F-B75C-B230CB71A4E6> /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ld
    Expected in:     <4C4C442A-5555-3144-A184-217C9A91A590> /Users/theo/Documents/llvm-project/install/Toolchains/LLVM20.0.0git.xctoolchain/usr/lib/libc++.1.0.dylib
  clang++: error: unable to execute command: Abort trap: 6
  clang++: error: linker command failed due to signal (use -v to see invocation)


  --- stderr
  thread 'main' panicked at helix-term/build.rs:7:14:
  Failed to compile tree-sitter grammars: 207 grammars failed to build

It's supposed to use ld.lld instead of ld, which is how I know it isn't working.

[theoparis]

I managed to fix it by removing the shared libraries from my toolchain for now.