Fix ia64 build failures in EFI platform

The MFC of the recent EFI work to stable/10 caused build breakage
under ia64.

It was not apparent that there was EFI code outside the EFI tree as
this is not the case in HEAD, however in stable/10 there is for ia64.

This change does the following:

• Re-enables libefi for ia64 under gcc.
• Adds the ignore for unsupported pragma's when building libefi for ia64.
• Adds the missing parameter to efi_handle_lookup in the ia64 loader.

This is a direct commit as ia64 is no longer supported after 10.x

Approved by: re (marius)
Sponsored by: Multiplay