[BOLT][NFC] Fix file-description comments

Summary: Fix comments at the start of source files.

(cherry picked from FBD33274597)

bolt/lib/Core/DebugData.cpp

@@ -1,4 +1,4 @@
-//===- DebugData.cpp - Representation and writing of debugging information. ==//
+//===- bolt/Core/DebugData.cpp - Debugging information handling -----------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
@@ -6,6 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 //
+// This file implements functions and classes for handling debug info.
+//
 //===----------------------------------------------------------------------===//
 
 #include "bolt/Core/DebugData.h"