Significant trailing whitespace in GNU Make

Makefile

# GNU Make 4.1

# the next line has no trailing whitespace
A=a
B=a#    no whitespace before the comment
C=a # some whitespace before the comment
# the next line has some trailing whitespace
D=a 

default:
	[ "$(A)" = "$(B)" ] && echo ok || echo ko # => ok
	[ "$(A)" = "$(C)" ] && echo ok || echo ko # => ko
	[ "$(A)" = "$(D)" ] && echo ok || echo ko # => ko
	[ "$(C)" = "$(D)" ] && echo ok || echo ko # => ok