then the best thing to do is transform them by substituting space with some other
character and then change them back again.
For example, the s+ and +s functions here change escaped spaces to + signs and back
again. You can then safely manipulate lists of file names using all the GNU Make
functions. Just be sure to remove the +'s before using these names in a rule.
s+ = $(subst \\ ,+,$1)
+s = $(subst +,\\ ,$1)
Here's a fuller example where a list of source files that contain escaped spaces is
transformed into a list of object files and then the object files are used to define the
prerequisites of the all rule.
SRCS := a\\ b.c c\\ d.c e\\ f.c
SRCS := $(call s+,$(SRCS))
OBJS := $(SRCS:.c=.o)
all: $(call +s,$(OBJS))