Attempt to ./configure with --disable-optimization on macOS prepends -O0 to $CFLAGS, however at the end it still has -g -O2.
I.e. in Makefile:
CFLAGS = -O0 -Wall -Wcast-align -Wshadow -Wstrict-prototypes -Wformat -Wno-format-y2k -Wformat-security -W -Wno-sign-compare -Wno-format-zero-length -Wno-missing-field-initializers -Wdeclaration-after-statement -Wvla -Wno-pointer-sign -Wpointer-arith -g -O2