CORE_DUMP_DEFAULT_ELF_HEADERS depends on ELF_CORE

Kernels that don't support ELF coredumps at all surely can't be supporting
new partial-segment flavored ELF coredumps ...  don't make folk answer
Kconfig questions about that flavor.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Acked-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>