GN: Normalize the build directory path

tools/gn/setup.cc

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "tools/gn/setup.h"
 
 #include <stdlib.h>
 #include <algorithm>
 #include <sstream>
 #include <utility>
@@ skipping 503 matching lines @@
   }
 
   if (scheduler_.verbose_logging())
     scheduler_.Log("Using source root", FilePathToUTF8(root_path));
   build_settings_.SetRootPath(root_path);
 
   return true;
 }
 
 bool Setup::FillBuildDir(const std::string& build_dir, bool require_exists) {
+#if defined(OS_POSIX)
+  // Expand all ./, ../, and symbolic links in build_dir.
+  char realpath_buf[PATH_MAX];
+  if (!realpath(build_dir.c_str(), realpath_buf)) {
+    Err(Location(), "Can't normalize the build directory path.",
+        strerror(errno)) .PrintToStdout();
+    return false;
+  }
+  const std::string build_dir_realpath = realpath_buf;
+#else
+  const std::string& build_dir_realpath = build_dir;
+#endif
+
   Err err;
   SourceDir resolved =
       SourceDirForCurrentDirectory(build_settings_.root_path()).
-    ResolveRelativeDir(Value(nullptr, build_dir), &err,
+    ResolveRelativeDir(Value(nullptr, build_dir_realpath), &err,
         build_settings_.root_path_utf8());
   if (err.has_error()) {
     err.PrintToStdout();
     return false;
   }
 
   if (scheduler_.verbose_logging())
     scheduler_.Log("Using build dir", resolved.value());
 
   if (require_exists) {
@@ skipping 146 matching lines @@
       if (err.has_error()) {
         err.PrintToStdout();
         return false;
       }
     }
     build_settings_.set_exec_script_whitelist(std::move(whitelist));
   }
 
   return true;
 }