Bug 1834678 - Change the llvm-config trick for cross-compilation. r=gfx-reviewers,gw

Contrary to ld64, lld doesn't ignore libraries it's given on the command
line, and -lLLVM-14 ends up as a link error when using lld.

So instead of relying on the flags llvm-config outputs to be kind of
ignored, we replace them at the source by wrapping llvm-config itself.

Differential Revision: https://phabricator.services.mozilla.com/D178900

gfx/wr/ci-scripts/etc/wr-darwin.meson

@@ -1,15 +1,5 @@
 [binaries]
-llvm-config = '/builds/worker/fetches/clang/bin/llvm-config'
-
-[properties]
-# When linking `libOSMesa.dylib` Meson uses options provided by `llvm-config`.
-# The binary for `llvm-config` in Firefox CI comes from a native Linux clang,
-# which gives the link options for the Linux libLLVM-11.so in the Linux clang.
-# However, we want to link against a native macOS clang's libLLVM.dylib, which
-# we have available in a separate directory.
-# Meson will still have -lLLVM-11 on the command line, but the linker will
-# only warn that it has the wrong format (because it's not for macOS).
-cpp_link_args = ['-L/builds/worker/fetches/clang-mac/clang/lib', '-lLLVM']
+llvm-config = '/builds/worker/fetches/clang-mac/clang/bin/llvm-config'
 
 [host_machine]
 system = 'darwin'

taskcluster/scripts/misc/wr-macos-cross-build-setup.sh

@@ -29,7 +29,10 @@ END_PKGCONFIG_WRAPPER
 chmod +x "${TARGET_TRIPLE}-pkg-config"
 popd
 
-export PATH="${MOZ_FETCHES_DIR}/rustc/bin:${MOZ_FETCHES_DIR}/cctools/bin:${MOZ_FETCHES_DIR}/clang/bin:${MOZ_FETCHES_DIR}/wrench-deps/meson:${PATH}"
+[ -d "${MOZ_FETCHES_DIR}/clang-mac/clang" ] && cat > ${MOZ_FETCHES_DIR}/clang-mac/clang/bin/llvm-config <<EOF_LLVM_CONFIG
+#!/bin/sh
+${MOZ_FETCHES_DIR}/clang/bin/llvm-config "\$@" | sed 's,${MOZ_FETCHES_DIR}/clang,${MOZ_FETCHES_DIR}/clang-mac/clang,g;s,-lLLVM-[0-9]\+,-lLLVM,g'
+EOF_LLVM_CONFIG
 
 # The x86_64-darwin11-ld linker from cctools requires libraries provided
 # by clang, so we need to set LD_LIBRARY_PATH for that to work.