livepatch-gcc: Ignore buildid.o

livepatch-gcc: Ignore buildid.o

Not all .o files generated by the Xen build need to be passed to
create-diff-object for analysis. The latest example is:

 Run create-diff-object on xen/arch/x86/efi/buildid.o
 Open base
 /usr/libexec/livepatch-build-tools/create-diff-object: ERROR: buildid.o: kpatch_create_section_list: 77: elf_getshdrnum

This file is special, as it does not contain any sections. It is
generated by objcopy from a magic string of bytes (see Xen commit
eee5909e9d1e x86/EFI: use less crude a way of generating the build ID),
which probably will never change. Therefore, livepatch-gcc should not
copy it to the output directory.

Signed-off-by: Raphael Ning <raphning@amazon.com>
Reviewed-by: Bjoern Doebel <doebel@amazon.de>
Reviewed-by: Martin Pohlack <mpohlack@amazon.de>
Reviewed-by: Ross Lagerwall <ross.lagerwall@citrix.com>