system-clang-format: Add IncludeBlocks: Preserve

As of [1], the Google format, which we default to, uses IncludeBlocks:
Regroup, which sorts all includes with <> and without .h into the top
group reserved for libc headers, e.g.:

+#include <android-base/properties.h>
+#include <android-base/strings.h>
 #include <ctype.h>
 #include <stdlib.h>
 #include <sys/system_properties.h>

 #include <iostream>

-#include <android-base/properties.h>
-#include <android-base/strings.h>

This is accurate to the Google C++ style guide, which states that
other library headers should be included with "", however we have a
strong tendency to use <> for these headers for Android, so we must
revert this change.

Note, clang-format allows regexes for creating the blocks as well,
however, short of including all possible libc headers, I don't think
there's a way to differentiate between <sys/wait.h> and
<other_lib/header.h>.

[1]:
https://github.com/llvm-mirror/clang/commit/62e3198c4f5490a1c60ba51d81fe2e1f0dc99135#diff-b689ebff2e51e675b346a88289e74542

Test: clang-format doesn't do the above.
Change-Id: Ifef605ffd6b4c8a36512377644e64ddd26b68a21