fix(aur): export RUSTFLAGS in PKGBUILD to actually pin ld.bfd

8383746 added .cargo/config.toml with rustflags=link-arg=-fuse-ld=bfd
but the chroot still linked with `-fuse-ld=lld`. cargo's RUSTFLAGS
env var takes precedence over [target.X.rustflags] in any
config.toml, so Arch's `extra/rust` pkg (which apparently sets its
own RUSTFLAGS to default rustc to LLD) was overriding the project
config silently.

Set `export RUSTFLAGS="-C link-arg=-fuse-ld=bfd"` directly in the
PKGBUILD's build() and check() functions. This is the highest-
precedence place — beats Arch's defaults, beats the project config,
beats any inherited env. Confirmed via the build-log chain in
build-logs/aur-test-20260513-132012.log: the link line still
contained `-fuse-ld=lld` despite the .cargo/config.toml landing in
the tarball.

`.cargo/config.toml` is kept (commit 8383746) so the local rustup
toolchain mirrors the chroot's linker. Belt-and-braces.

Re-run `just aur-local-test owlry`. Expected link line should now
contain `-fuse-ld=bfd` and the build should complete.

aur/owlry/PKGBUILD

@@ -86,6 +86,15 @@ build() {
     cd "owlry"
     export RUSTUP_TOOLCHAIN=stable
     export CARGO_TARGET_DIR=target
+    # Force GNU ld.bfd. Arch's `extra/rust` defaults rustc to `-fuse-ld=lld`,
+    # and LLD's single-pass arg processing can't satisfy `-llua5.4` because
+    # mlua-sys+lua-src emit the `-l` flag before their `-L $OUT_DIR/lib`
+    # search path in the final link line (cargo:rustc-link-lib emitted
+    # before cargo:rustc-link-search). BFD does multi-pass and finds the
+    # archive regardless. RUSTFLAGS env-var beats any cargo config rustflags,
+    # which is necessary here because Arch's rust pkg appears to set its own
+    # RUSTFLAGS that we need to fully override.
+    export RUSTFLAGS="-C link-arg=-fuse-ld=bfd"
     # 'full' enables every optional provider — the AUR binary is the
     # batteries-included experience. cargo install consumers can still opt
     # to --no-default-features and pick their own subset.
@@ -96,6 +105,7 @@ check() {
     cd "owlry"
     export RUSTUP_TOOLCHAIN=stable
     export CARGO_TARGET_DIR=target
+    export RUSTFLAGS="-C link-arg=-fuse-ld=bfd"
     cargo test --frozen --release --features full
 }