Recreate usrmerge links in the x64 sysroot.

.gitea/scripts/install-linux-build-dependencies.sh

@@ -80,6 +80,12 @@ case "$target" in
             sudo dpkg-deb --extract "$package" "$sysroot"
         done
 
+        # Recreate Ubuntu's merged-/usr root links. libc development linker
+        # scripts refer to /lib paths, while libc6 stores the files in
+        # /usr/lib; --sysroot expects the same links as a complete rootfs.
+        sudo ln -s usr/lib "$sysroot/lib"
+        sudo ln -s usr/lib64 "$sysroot/lib64"
+
         # Architecture-independent development packages may already be
         # installed on the host, so apt does not download them again. Their
         # pkg-config files contain no host binaries and are safe to reuse with

crates/bds-ui/tests/packaging_assets.rs

@@ -195,6 +195,8 @@ fn tagged_releases_are_built_and_packaged_with_rust_tools() {
         "Architectures: arm64",
         "--download-only",
         "dpkg-deb --extract",
+        "ln -s usr/lib \"$sysroot/lib\"",
+        "ln -s usr/lib64 \"$sysroot/lib64\"",
         "/usr/share/pkgconfig/.",
         "/opt/ruds-x64-sysroot",
     ] {