Fix --noenable_runfiles on non Windows (#158)

I don't think there's much of a reason users should ever pass this flag,
but it's easy enough to support.

Fixes https://github.com/keith/buildifier-prebuilt/issues/91

runner.bash.template

diff --git a/runner.bash.template b/runner.bash.template
index e181354..031dac1 100644
--- a/runner.bash.template
+++ b/runner.bash.template
@@ -6,8 +6,50 @@
 ARGS=@@ARGS@@
 WORKSPACE="@@WORKSPACE@@"
 
-# Get the absolute path to the buildifier executable
-buildifier_short_path=$(readlink "$BUILDIFIER_SHORT_PATH")
+function resolve_runfile() {
+  local path=$1
+  local runfiles_path=${path#../}
+  local candidate
+  local manifest
+  local line
+
+  if [[ -e "$path" ]]; then
+    realpath "$path"
+    return 0
+  fi
+
+  if [[ -n "${RUNFILES_DIR:-}" ]]; then
+    candidate="${RUNFILES_DIR}/${runfiles_path}"
+    if [[ -e "$candidate" ]]; then
+      realpath "$candidate"
+      return 0
+    fi
+  fi
+
+  for manifest in \
+    "${RUNFILES_MANIFEST_FILE:-}" \
+    "$0.runfiles_manifest" \
+    "$0.exe.runfiles_manifest" \
+    "$0.runfiles/MANIFEST"; do
+    [[ -n "$manifest" && -f "$manifest" ]] || continue
+    while IFS= read -r line; do
+      if [[ "$line" == "${runfiles_path} "* ]]; then
+        printf '%s\n' "${line#* }"
+        return 0
+      elif [[ "$line" == "$runfiles_path" ]]; then
+        printf '%s\n' "$runfiles_path"
+        return 0
+      fi
+    done < "$manifest"
+  done
+
+  return 1
+}
+
+if ! buildifier_short_path=$(resolve_runfile "$BUILDIFIER_SHORT_PATH"); then
+  echo "Unable to locate buildifier runfile: $BUILDIFIER_SHORT_PATH" >&2
+  exit 1
+fi
 
 # Use TEST_WORKSPACE to determine if the script is being ran under a test
 if [[ -n "${TEST_WORKSPACE+x}" && -z "${BUILD_WORKSPACE_DIRECTORY+x}" ]]; then

tests/buildifier/buildifier_test.sh

diff --git a/tests/buildifier/buildifier_test.sh b/tests/buildifier/buildifier_test.sh
index 118474a..78a4e54 100755
--- a/tests/buildifier/buildifier_test.sh
+++ b/tests/buildifier/buildifier_test.sh
@@ -239,11 +239,6 @@
 }
 
 function test_buildifier_check_without_runfiles() {
-    if ! is_windows; then
-        # https://github.com/keith/buildifier-prebuilt/issues/91
-        echo "SKIPPED --noenable_runfiles only supported by buildifier_prebuilt on windows"
-        return 0
-    fi
     create_simple_workspace >"${TEST_log}"
 
     expect_buildifier_check_failure --noenable_runfiles
@@ -261,11 +256,6 @@
 }
 
 function test_buildifier_fix_without_runfiles() {
-    if ! is_windows; then
-        # https://github.com/keith/buildifier-prebuilt/issues/91
-        echo "SKIPPED --noenable_runfiles only supported by buildifier_prebuilt on windows"
-        return 0
-    fi
     create_simple_workspace >"${TEST_log}"
     cp BUILD orig-BUILD-file