[PATCH v4 0/2] Makefile: link osxkeychain helper against Rust

This series improves macOS build reliability and distribution support when Rust is enabled in the Git build system. It addresses two distinct challenges: a parallel build race condition in git-credential-osxkeychain and support for macOS Universal Binaries (multi-architecture distribution).

Why This Series is Needed =========================

 1. Parallel Build Race Condition ("make -j"): While commit 522ea8ef7d
    ("osxkeychain: fix build with Rust") updated the link command for
    git-credential-osxkeychain to pass $(LIBS), it omitted $(RUST_LIB) from
    the target prerequisite list. When running a parallel build ("make -j")
    from a clean working tree, Make can attempt to link
    git-credential-osxkeychain before Cargo has finished compiling
    libgitcore.a, causing linker failures.

 2. macOS Universal Binary (lipo) Support: On macOS, Universal Binaries
    bundle native executable code for multiple architectures (Intel x86_64
    and Apple Silicon arm64) into a single file. This is standard practice
    for macOS distribution and CI packaging (such as Burrito, Homebrew, and
    Git's macOS CI runners), allowing a single artifact to run natively
    across all Macs without Rosetta translation.

While Apple's C compiler (clang) natively supports universal builds by passing "-arch x86_64 -arch arm64" in CFLAGS and LDFLAGS, Cargo and rustc do not support multiple "-arch" flags in a single invocation. Instead, Cargo must be invoked separately for each target triple ("--target x86_64-apple-darwin" and "--target aarch64-apple-darwin"). This series bridges that gap.

Overview of Patches ===================

 * Patch 1: Makefile: add $(RUST_LIB) prerequisite to osxkeychain Adds
   $(RUST_LIB) as a prerequisite dependency to the osxkeychain target,
   eliminating the parallel build race condition. Additionally, wraps the
   definitions of $(RUST_LIB) and the "rust" build target in "ifndef
   NO_RUST" so that disabling Rust cleanly makes the dependency a no-op.

 * Patch 2: Makefile: support universal macOS builds via RUST_TARGETS Allows
   users to specify space-separated target triples in RUST_TARGETS.
   Introduces declarative pattern rules (target/%/...) to compile each
   target slice via Cargo, and uses "lipo" (part of the mandatory Xcode
   Command Line Tools) to combine the resulting static archives into a
   universal library at target/release/libgitcore.a. Uses
   mkdir_p_parent_template to guarantee directory creation before lipo.

Changes since v2:

 * Split the original combined commit into a two-patch series to separate
   prerequisite bug fixes from Universal Binary features.
 * Added $(call mkdir_p_parent_template) prior to invoking lipo to guarantee
   that parent target directories exist.
 * 

Shardul Natu (2):
  Makefile: add $(RUST_LIB) prerequisite to osxkeychain
  Makefile: support universal macOS builds via RUST_TARGETS

 Makefile | 46 +++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 41 insertions(+), 5 deletions(-)

base-commit: 602f6c329a7d99df269d382df353b4e1bbbbd8aa
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-2288%2Fkiranani%2Fnext-v4
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-2288/kiranani/next-v4
Pull-Request: https://github.com/git/git/pull/2288

Range-diff vs v3:

 1:  41de7d391a = 1:  41de7d391a Makefile: add $(RUST_LIB) prerequisite to osxkeychain
 2:  257f5ef42f ! 2:  88fc2e0bd8 Makefile: support universal macOS builds via RUST_TARGETS
     @@ Makefile: $(LIB_FILE): $(LIB_OBJS)
      +	$(QUIET_CARGO)cargo build $(CARGO_ARGS) --target $*
      +
      +$(RUST_LIB): $(RUST_MEMBER_LIBS)
     -+	@$(call mkdir_p_parent_template)
     ++	$(call mkdir_p_parent_template)
      +	$(QUIET_GEN)\
     -+	if [ $(words $(RUST_TARGETS)) -gt 1 ]; then \
     ++	if test $(words $(RUST_TARGETS)) -gt 1; \
     ++	then \
      +		lipo -create $^ -output $@; \
      +	else \
      +		cp $< $@; \