Fix problem reported by Ree: convert 'x86_64' machine type to 'x64'.

install/GNUmakefile

@@ -71,6 +71,9 @@ os      :=      $(shell echo $(os) | tr '[A-Z]' '[a-z]' | tr ' ' '_')
 
 machine         :=      $(shell if uname -m | egrep -v "(i[3456789]|x)86" > /dev/null; then uname -m | tr "[A-Z]" "[a-z]" | tr " " "_" ; fi)
 machine		:=	$(shell if uname -m | egrep "64" > /dev/null; then uname -m | tr "[A-Z]" "[a-z]" | tr " " "_" ; else echo $(machine) ; fi)
+ifeq ($(machine),x86_64)
+ machine        := 	x64
+endif
 ifeq ($(machine),)
  machine        :=      $(os)
 else