Thank you.
For the -fno-sanitiser=undefined this was suggested by LLM. I researched about it and found this question in this forum, so I decided to put a comment and see what others suggest.
The Makefile contains
# WITH_ASAN builds with sanitizers
ifeq ($(WITH_ASAN),1)
override CFLAGS += -fsanitize=address -g
override LDFLAGS += -fsanitize=address
endif
Which I believe is for that flag. Using address instead of undefined compiles successfully. Since I’m not sure what I’m doing, I just left a comment to revisit later.