Sync with make-rules repo

mk/functions.mk

@@ -5,3 +5,10 @@ rwildcard=$(foreach d,$(wildcard $1*),$(call rwildcard,$d/,$2) $(filter $(subst
 # Given a file name, produce the corresponding dependency file
 # (e.g. ‘foo/bar.o’ becomes ‘foo/.bar.o.dep’).
 filename-to-dep = $(dir $1).$(notdir $1).dep
+
+# Return the full path to a program by looking it up in $PATH, or the
+# empty string if not found.
+find-program = $(shell for i in $$(IFS=: ; echo $$PATH); do p=$$i/$(strip $1); if [ -e $$p ]; then echo $$p; break; fi; done)
+
+# Remove trailing slash.
+add-trailing-slash = $(patsubst %/,%,$(1))/