Allow for easier override from make's commandline.
--- a/Make.defaults
+++ b/Make.defaults
@@ -64,7 +64,7 @@ TOPDIR  =
 ALLSUBDIRS = ia32 ia64 x86_64 fs choosers devschemes tools
 
 HOSTARCH   = $(shell dpkg-architecture -qDEB_BUILD_ARCH | sed s,i[3456789]86,ia32, | sed s,amd64,x86_64, )
-ARCH	   := $(shell dpkg-architecture -qDEB_BUILD_ARCH | sed s,i[3456789]86,ia32, | sed s,amd64,x86_64, )
+ARCH	   = $(shell dpkg-architecture -qDEB_BUILD_ARCH | sed s,i[3456789]86,ia32, | sed s,amd64,x86_64, )
 INCDIR	   = -I. -I$(TOPDIR) -I$(EFIINC) -I$(EFIINC)/$(ARCH) -I$(EFIINC)/protocol -I$(TOPDIR)/efi110
 CPPFLAGS   = -DCONFIG_$(ARCH)