header-checker: Code cleanup

This commit cleans up several whitespaces nits, re-indent the code,
remove unnecessary data member initializers, and add missing header
guards.

Test: ./tests/test.py
Change-Id: Ibc355441aaa110280b263c5c3d8fc766941b08af

vndk/tools/header-checker/merge-abi-diff/src/merge_abi_diff.cpp

@@ -12,6 +12,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+#include "header_abi_util.h"
+
 #pragma clang diagnostic push
 #pragma clang diagnostic ignored "-Wunused-parameter"
 #pragma clang diagnostic ignored "-Wnested-anon-types"
@@ -19,17 +21,15 @@
 #include "abi_diff.pb.h"
 #pragma clang diagnostic pop
 
-#include <header_abi_util.h>
+#include <google/protobuf/text_format.h>
+#include <google/protobuf/io/zero_copy_stream_impl.h>
 
 #include <llvm/Support/CommandLine.h>
 #include <llvm/Support/raw_ostream.h>
 
-#include <google/protobuf/text_format.h>
-#include <google/protobuf/io/zero_copy_stream_impl.h>
-
-#include <memory>
 #include <fstream>
 #include <iostream>
+#include <memory>
 #include <string>
 #include <vector>