The current Makefile fragment is: ifeq (,$(findstring -DLLDB_DISABLE_PYTHON,$(CXXFLAGS))) BUILT_SOURCES := LLDBWrapPython.cpp endif which looks correct to me: if -DLLDB_DISABLE_PYTHON is not set then findstring returns an empty string, ifeq is true, and BUILT_SOURCES gets LLDBWrapPython.cpp.