signal11/hidapi — comment on commit 56a0bf9ada12da0ffa2b637ab180a01be621003c
File:  line 0
By LudovicRousseau:

Implicit rules are, in general, more powerfull. For example in the present case the implicit rules is:

%.o: %.c
$(COMPILE.c) $(OUTPUT_OPTION) $<

with
COMPILE.c = $(CC) $(CFLAGS) $(CPPFLAGS) $(TARGET_ARCH) -c
OUTPUT_OPTION = -o $@

Your explicit rule do not use $(CPPFLAGS) so it is not possible to do:
$ CPPFLAGS=myflag make