fix flex build on Cygwin

package/flex/Makefile

@@ -10,7 +10,7 @@ PKG_HASH:=		bf693433a3effe6b1f42e44abd787491e4e213984b1859545b92267a86088dd3
 PKG_DESCR:=		fast lexical analyzer
 PKG_SECTION:=		dev/tools
 PKG_BUILDDEP:=		m4-host
-HOST_BUILDDEP:=		m4-host
+HOST_BUILDDEP:=		patch-host m4-host
 PKG_URL:=		http://flex.sourceforge.net/
 PKG_SITES:=		$(MASTER_SITE_SOURCEFORGE:=flex/)
 PKG_OPTS:=		dev

package/flex/patches/patch-Makefile_in

@@ -0,0 +1,13 @@
+--- flex-2.5.37.orig/Makefile.in	2012-08-03 19:07:25.000000000 +0200
++++ flex-2.5.37/Makefile.in	2015-04-03 22:29:28.399676900 +0200
+@@ -1234,10 +1234,6 @@ indent:
+ 	done \
+ 	fi
+ 
+-install-exec-hook:
+-	cd $(DESTDIR)/$(bindir) && \
+-		$(LN_S) -f flex$(EXEEXT) flex++$(EXEEXT)
+-
+ .PHONY: ChangeLog tags indent
+ 
+ # Tell versions [3.59,3.63) of GNU make to not export all variables.