Resolve x64 libc links through the sysroot.

.gitea/workflows/release.yml

@@ -139,7 +139,7 @@ jobs:
       CC_x86_64_unknown_linux_gnu: x86_64-linux-gnu-gcc
       CXX_x86_64_unknown_linux_gnu: x86_64-linux-gnu-g++
       CARGO_TARGET_X86_64_UNKNOWN_LINUX_GNU_LINKER: x86_64-linux-gnu-gcc
-      CARGO_TARGET_X86_64_UNKNOWN_LINUX_GNU_RUSTFLAGS: -C link-arg=-Wl,-rpath,$ORIGIN -L native=/opt/ruds-x64-sysroot/usr/lib/x86_64-linux-gnu -L native=/opt/ruds-x64-sysroot/lib/x86_64-linux-gnu
+      CARGO_TARGET_X86_64_UNKNOWN_LINUX_GNU_RUSTFLAGS: -C link-arg=--sysroot=/opt/ruds-x64-sysroot -C link-arg=-Wl,-rpath,$ORIGIN -L native=/opt/ruds-x64-sysroot/usr/lib/x86_64-linux-gnu -L native=/opt/ruds-x64-sysroot/lib/x86_64-linux-gnu
       PKG_CONFIG_ALLOW_CROSS: "1"
       PKG_CONFIG_LIBDIR: /opt/ruds-x64-sysroot/usr/lib/x86_64-linux-gnu/pkgconfig:/opt/ruds-x64-sysroot/usr/lib/pkgconfig:/opt/ruds-x64-sysroot/usr/share/pkgconfig
       PKG_CONFIG_SYSROOT_DIR: /opt/ruds-x64-sysroot

crates/bds-ui/tests/packaging_assets.rs

@@ -230,6 +230,10 @@ fn tagged_releases_are_built_and_packaged_with_rust_tools() {
         "foreign libraries must only be downloaded after enabling multiarch"
     );
     assert!(workflow.contains("PKG_CONFIG_SYSROOT_DIR: /opt/ruds-x64-sysroot"));
+    assert!(
+        workflow.contains("link-arg=--sysroot=/opt/ruds-x64-sysroot"),
+        "the cross-linker must resolve absolute libc linker-script paths inside the x64 sysroot"
+    );
 
     let workspace_manifest = fs::read_to_string(workspace.join("Cargo.toml")).unwrap();
     let core_manifest = fs::read_to_string(workspace.join("crates/bds-core/Cargo.toml")).unwrap();