loader/efi: Only include interpreter's linker script

For safety, only include the interpreter's linker script. Note that the
simple loader doesn't have one, but it's not an error to copy a ELF
section that does not exist. No functional change, however.

Sponsored by:		Netflix
Reviewed by:		tsoome, kevans
Differential Revision:	https://reviews.freebsd.org/D44064

stand/efi/loader/Makefile

@@ -117,7 +117,7 @@ ${LOADER}.efi: ${PROG}
 	${OBJCOPY} -j .peheader -j .text -j .sdata -j .data \
 		-j .dynamic -j .dynsym -j .rel.dyn \
 		-j .rela.dyn -j .reloc -j .eh_frame -j set_Xcommand_set \
-		-j set_X4th_compile_set -j set_Xlua_compile_set \
+		-j set_X${LOADER_INTERP}_compile_set \
 		--output-target=${EFI_TARGET} ${.ALLSRC} ${.TARGET}
 
 LIBEFI=		${BOOTOBJ}/efi/libefi/libefi.a