Linux: engines and apps build in an Ubuntu 26.04 container, glibc 2.43 at most (L1.4)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

scripts/build-git.sh

@@ -38,6 +38,6 @@ if [ "$(cat "$out/.flags" 2>/dev/null)" != "$flags" ]; then
   rm -rf "$out"
 fi
 # shellcheck disable=SC2086
-make -C "$src" $flags -j"$jobs" install
+env -u CARGO_TARGET_DIR make -C "$src" $flags -j"$jobs" install # Git's Rust uses its target/
 echo "$flags" >"$out/.flags"
 "$out/bin/git" --version