make 3.81 intentionally removed support for DOS paths; use
make 3.80 or the newer version (make-3.81-2?).
If you're using cygpath in a mixed Windows/Unix environment, you'll want to wrap these calls in a portable function:
ifdef COMSPEC
cygpath-mixed = $(shell cygpath -m "$1")
cygpath-unix = $(shell cygpath -u "$1")
drive-letter-to-slash = /$(subst :,,$1)
else
cygpath-mixed = $1
cygpath-unix = $1
drive-letter-to-slash = $1
endif
