[build] Use -malign-double to build 32-bit UEFI binaries

The EDK2 codebase uses -malign-double for 32-bit builds, which causes
64-bit integers to be naturally aligned.  This affects the layout of
some structures (including EFI_BLOCK_IO_MEDIA).

This mirrors wimboot commit 7b8f39d ("[build] Fix building of 32-bit
UEFI version").

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/arch/i386/Makefile.efi

@@ -4,6 +4,10 @@
 #
 ELF2EFI		= $(ELF2EFI32)
 
+# Use EFI ABI
+#
+CFLAGS		+= -malign-double
+
 # Include generic EFI Makefile
 #
 MAKEDEPS	+= arch/x86/Makefile.efi