This BUILD_CONFIG option builds checks that toggling debug

information generation doesn't affect the generated object code.

It is very lightweight: in addition to not performing any additional

compilation (unlike bootstrap-debug-lean), it actually speeds up

stage2, for no debug information is generated when compiling with

the unoptimized stage1.

For more thorough testing, see bootstrap-debug-lean.mk

STAGE2_CFLAGS += -gtoggle do-compare = $(SHELL) $(srcdir)/contrib/compare-debug $$f1 $$f2