Add a helper run_lit.sh for interactive debugging.

tools/run_lit.sh

@@ -0,0 +1,35 @@
+#!/bin/bash
+# Runs lit-based tests by properly translating paths to the build directory.
+# Example:
+#   ./tools/run_lit.sh test/Dialect -v
+set -e
+
+td="$(realpath $(dirname $0)/..)"
+build_dir="$td/build"
+install_mlir="$td/install-mlir"
+build_mlir="$td/build-mlir"
+
+lit_exe="$build_mlir/bin/llvm-lit"
+if ! [ -f "$lit_exe" ]; then
+  echo "Could not find lit: $lit_exe"
+  exit 1
+fi
+
+declare -a lit_args
+for i in "$@"; do
+  if [[ ${i:0:1} = "-" ]] || [[ ${i:0:1} = "/" ]]; then
+    lit_args+=("$i")
+  else
+    if ! [ -e "$i" ]; then
+      echo "Specified lit input does not exist: $i"
+      exit 1
+    fi
+    test_local_path="$(realpath $i)"
+    # Replace the src prefix with the build dir.
+    test_build_path="$build_dir/${test_local_path##$td/}"
+    lit_args+=("$test_build_path")
+  fi
+done
+
+set -x
+cd $build_dir/test && python3 "$lit_exe" ${lit_args[@]}