Rename DEBUG macro to LLVM_DEBUG.
    
The DEBUG() macro is very generic so it might clash with other projects.
The renaming was done as follows:
- git grep -l 'DEBUG' | xargs sed -i 's/\bDEBUG\s\?(/LLVM_DEBUG(/g'
- git diff -U0 master | ../clang/tools/clang-format/clang-format-diff.py -i -p1 -style LLVM
- Manual change to APInt
- Manually chage DOCS as regex doesn't match it.

In the transition period the DEBUG() macro is still present and aliased
to the LLVM_DEBUG() one.

Differential Revision: https://reviews.llvm.org/D43624

llvm-svn: 332240
diff --git a/llvm/lib/IR/ConstantsContext.h b/llvm/lib/IR/ConstantsContext.h
index 6585304..e9f31e4 100644
--- a/llvm/lib/IR/ConstantsContext.h
+++ b/llvm/lib/IR/ConstantsContext.h
@@ -695,7 +695,9 @@
     return nullptr;
   }
 
-  void dump() const { DEBUG(dbgs() << "Constant.cpp: ConstantUniqueMap\n"); }
+  void dump() const {
+    LLVM_DEBUG(dbgs() << "Constant.cpp: ConstantUniqueMap\n");
+  }
 };
 
 } // end namespace llvm