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/CodeGen/GlobalMerge.cpp b/llvm/lib/CodeGen/GlobalMerge.cpp
index be4ba4d..cda5861 100644
--- a/llvm/lib/CodeGen/GlobalMerge.cpp
+++ b/llvm/lib/CodeGen/GlobalMerge.cpp
@@ -442,8 +442,8 @@
   Type *Int32Ty = Type::getInt32Ty(M.getContext());
   auto &DL = M.getDataLayout();
 
-  DEBUG(dbgs() << " Trying to merge set, starts with #"
-               << GlobalSet.find_first() << "\n");
+  LLVM_DEBUG(dbgs() << " Trying to merge set, starts with #"
+                    << GlobalSet.find_first() << "\n");
 
   ssize_t i = GlobalSet.find_first();
   while (i != -1) {