x86: Regex support and known-movable symbols for relocs, fix _end

This adds a new category of symbols to the relocs program: symbols
which are known to be relative, even though the linker emits them as
absolute; this is the case for symbols that live in the linker script,
which currently applies to _end.

Unfortunately the previous workaround of putting _end in its own empty
section was defeated by newer binutils, which remove empty sections
completely.

This patch also changes the symbol matching to use regular expressions
instead of hardcoded C for specific patterns.

This is a decidedly non-minimal patch: a modified version of the
relocs program is used as part of the Syslinux build, and this 	is
basically a backport to Linux of some of those changes; they have
thus been well tested.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
LKML-Reference: <4AF86211.3070103@zytor.com>
Acked-by: Michal Marek <mmarek@suse.cz>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>