[NFC] format c-index-test.c

to separate formatting changes from a functional fix later
also inlcude CXDiagnostic and CXFile

Author: metaflow

clang/tools/c-index-test/c-index-test.c

@@ -2,7 +2,9 @@
 
 #include "clang-c/BuildSystem.h"
 #include "clang-c/CXCompilationDatabase.h"
+#include "clang-c/CXDiagnostic.h"
 #include "clang-c/CXErrorCode.h"
+#include "clang-c/CXFile.h"
 #include "clang-c/CXSourceLocation.h"
 #include "clang-c/CXString.h"
 #include "clang-c/Documentation.h"