ppc-aix core file relocation.

The current code attempts to provide relocation support when debugging
core files via the rs6000_xfer_partial method of the rs6000-nat
target_ops vector. However, this target_ops vector does not get pushed
on the target stack at all when debugging core files, thus bypassing
completely that part of the code.

This patch fixes the problem by extending corelow's core_xfer_partial
into handling the TARGET_OBJECT_LIBRARIES_AIX object.

gdb/ChangeLog:

	* gdbarch.sh (core_xfer_shared_libraries_aix): New method.
	* gdbarch.h, gdbarch.c: Regenerate.
	* corelow.c (core_xfer_partial): Add TARGET_OBJECT_LIBRARIES_AIX
	handling.

	* rs6000-aix-tdep.h: New file.
	* Makefile.in (HFILES_NO_SRCDIR): Add rs6000-aix-tdep.h.
	* rs6000-aix-tdep.c: Include "rs6000-aix-tdep.h" and
	"xml-utils.h".
	(struct field_info, struct ld_info_desc): New types.
	(ld_info32_desc, ld_info64_desc): New static constants.
	(struct ld_info): New type.
	(rs6000_aix_extract_ld_info): New function.
	(rs6000_aix_shared_library_to_xml): Likewise.
	(rs6000_aix_ld_info_to_xml): Likewise.
	(rs6000_aix_core_xfer_shared_libraries_aix): Likewise.
	(rs6000_aix_init_osabi): Add call to
	set_gdbarch_core_xfer_shared_libraries_aix.
	* rs6000-nat.c: Add "rs6000-aix-tdep.h" include.
	Remove "xml-utils.h" include.
	(LdInfo): Delete typedef.
	(ARCH64_DECL, LDI_FIELD, LDI_NEXT, LDI_FD, LDI_FILENAME):
	Delete macros.
	(rs6000_ptrace_ldinfo): Change return type to gdb_byte *.
	Adjust code accordingly.
	(rs6000_core_ldinfo): Delete, folded into
	rs6000_aix_core_xfer_shared_libraries_aix.
	(rs6000_xfer_shared_library): Delete.
	(rs6000_xfer_shared_libraries): Reimplement.
Remove forward enum declaration in utils.h.

These forward declarations are a GNU extension, and they trigger
a build warning when the compiler does not support it.

gdb/ChangeLog:

        * utils.h: #include "exceptions.h".
        (enum errors): Remove partial declaration.