Quiet the cosmetic zig linker_messages warning on the musl build

The musl release build now links cleanly through cargo-zigbuild, but rustc's
new linker_messages lint echoed zig's "ignoring deprecated linker optimization
setting '1'" note — zig's linker declining the -O1 GNU-ld flag Rust passes. It
is cosmetic and the binary is correct, so allow that one lint, scoped to the
zig build step only. macOS and Windows keep full linker diagnostics, and a real
link error still fails the build.

No behaviour change to the produced binaries; takes effect on the next tag.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.github/workflows/release.yml

@@ -88,6 +88,12 @@ jobs:
         run: |
           set -euo pipefail
           if [[ "${{ matrix.zig }}" == "true" ]]; then
+            # zig's linker ignores the `-O1` GNU-ld optimization flag Rust passes
+            # and says so on stderr, which rustc now surfaces as a linker_messages
+            # warning. It is cosmetic — the binary is correct — so quiet just that
+            # one lint to keep the musl build log clean. A real link error still
+            # fails the build.
+            export RUSTFLAGS="${RUSTFLAGS:-} -A linker_messages"
             cargo zigbuild --release --locked --target "${{ matrix.target }}" --bin tsunagi
           else
             cargo build --release --locked --target "${{ matrix.target }}" --bin tsunagi