message: improve backtraces
diff: @@ -4,7 +4,8 @@ TARGET=$(rustc --print target-spec-json -Z unstable-options | jq '.["llvm-target
  SYSROOT=$(rustc --print sysroot)
  # We set the rpath so that Miri finds the private rustc libraries it needs.
  # We enable debug-assertions to get tracing.
  -export RUSTFLAGS="-C link-args=-Wl,-rpath,$SYSROOT/lib/rustlib/$TARGET/lib -C debug-assertions"
  +# We enable line-only debuginfo for backtraces.
  +export RUSTFLAGS="-C link-args=-Wl,-rpath,$SYSROOT/lib/rustlib/$TARGET/lib -C debug-assertions -C debuginfo=1"
  COMMAND="$1"
  shift
  