GNUmakefile: prefer system ln.exe at make

Author: oech3

GNUmakefile

@@ -71,7 +71,7 @@ OS ?= $(shell uname -s)
 # Windows does not allow symlink by default.
 # Allow to override LN for AppArmor.
 ifeq ($(OS),Windows_NT)
-	LN ?= ln -f
+	LN ?= $(shell command -v ln) -f
 endif
 LN ?= ln -sf