The DEBUG() macro is too generic so it might clash with other projects.
I noticed in include/llvm/DebugInfo/PDB/DIA/DIASupport.h a comment expressing interest in changing DEBUG() to LLVM_DEBUG() so I decided to give it a go.
This is the command I used to do the replacement:
git grep -l 'DEBUG' | xargs sed -i 's/\bDEBUG\s\?(/LLVM_DEBUG(/g'
Then I manually adjusted the DEBUG macro push/pop uses in APInt.cpp and DIASupport.h
Also, formatted the patch with git diff -U0 master | ../clang/tools/clang-format/clang-format-diff.py -i -p1 -style LLVM