I have download xen unstable tree which include your efi patch,and try to build xen.efi ,but there only have xen.gz ,don't have xen.efi .I find the file xen\arch\x86\efi\disable have report some error : ld don't  support -m i386pep.  my gcc version is 4.6.1.
if modify the i386pep to elf_x86_64 ,the build can continue ,and report other error --subsystem=10 and --image-base=0xffff82c480000000 unrecognized.
do you have any suggestion about that?  thank you very much!

the detail is follow.
ld: unrecognized emulation mode: i386pep
Supported emulations: elf_x86_64 elf32_x86_64 elf_i386 i386linux elf_l1om