Use commit_id.py on Windows, and handle missing git.

This allows us to delete the Windows batch file.

Changes the commit_id script to take the working directory so that it
can be called from a different working directory than the angle
repository is in.

Renames the generated commit header to angle_commit.h. This is being
written to the shared generated code directory for the entire build,
and "commit.h" is insufficiently unique.

BUG=angle:669

Change-Id: I35e80411a7e8ba1e02ce3f6a4fc54ed4dbc918f3
Reviewed-on: https://chromium-review.googlesource.com/202048
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>
diff --git a/src/commit.h b/src/commit.h
new file mode 100644
index 0000000..4c89a65
--- /dev/null
+++ b/src/commit.h
@@ -0,0 +1,14 @@
+//
+// Copyright (c) 2014 The ANGLE Project Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+//
+// commit.h:
+//   This is a default commit hash header, when git is not available.
+//
+
+#define ANGLE_COMMIT_HASH "unknown hash"
+#define ANGLE_COMMIT_HASH_SIZE 12
+#define ANGLE_COMMIT_DATE "unknown date"
+
+#define ANGLE_DISABLE_PROGRAM_BINARY_LOAD