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/Target/Mips/MipsSubtarget.cpp b/llvm/lib/Target/Mips/MipsSubtarget.cpp
index 1cbffbf..a4d159c 100644
--- a/llvm/lib/Target/Mips/MipsSubtarget.cpp
+++ b/llvm/lib/Target/Mips/MipsSubtarget.cpp
@@ -234,7 +234,8 @@
 }
 
 bool MipsSubtarget::useConstantIslands() {
-  DEBUG(dbgs() << "use constant islands " << Mips16ConstantIslands << "\n");
+  LLVM_DEBUG(dbgs() << "use constant islands " << Mips16ConstantIslands
+                    << "\n");
   return Mips16ConstantIslands;
 }