Fix linters on non-fb machines

Summary:
Our linters assume that clang-format is installed at /mnt/vol/engshare/admin/scripts/clang-format and flint is installed at /home/engshare/tools/flint. This makes them fail on non-fb machines. This change will:
* if clang-format is not on a specified path, it will try running generic clang-format. Linters will still fail if clang-format is not installed, but this shouldn't be a big issue, since it's pretty easy to install it.
* flint will not be run if /home/engshare/tools/flint is not present

Test Plan: Made a change on a mac machine. Ran `arc lint`. No failures observed.

Reviewers: aekmekji, yhchiang

Reviewed By: yhchiang

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D44031

arcanist_util/cpp_linter/FbcodeClangFormatLinter.php

@@ -35,9 +35,15 @@ final class FbcodeClangFormatLinter extends BaseDirectoryScopedFormatLinter {
       $args .= " --lines=$key:$key";
     }
 
+    $binary = self::CLANG_FORMAT_BINARY;
+    if (!file_exists($binary)) {
+      // trust the $PATH
+      $binary = "clang-format";
+    }
+
     return new ExecFuture(
       "%s %s $args",
-      self::CLANG_FORMAT_BINARY,
+      $binary,
       $this->getEngine()->getFilePathOnDisk($path));
   }
 

arcanist_util/cpp_linter/FbcodeCppLinter.php

@@ -11,6 +11,9 @@ class FbcodeCppLinter extends ArcanistLinter {
   private $rawLintOutput = array();
 
   public function willLintPaths(array $paths) {
+    if (!file_exists(self::FLINT)) {
+      return;
+    }
     $futures = array();
     foreach ($paths as $p) {
       $lpath = $this->getEngine()->getFilePathOnDisk($p);