Patch from Will Schmidt <willschm@us.ibm.com>:

These changes enable support of PPC64 architecture.
* config/powerpc/ppc64linux.mh: New file.
* config/powerpc/ppc64linux.mt: New file.
* config/powerpc/tm-ppc64linux.h: New file.
* ppc64-linux-tdep.c: New file.
* configure.host: Add clause for powerpc64-*-linux*
* configure.tgt: Add clause for powerpc64-*-linux*
* elfread.c (record_minimal_symbol_and_info): If
DROP_TEXT_NAME_PREFIX_CHAR is #defined, then drop a leading
instance of that char from the names of text symbols.
(elf_symtab_read): If SKIP_DATA_IN_OPD is #defined, ignore data
symbols in the .opd section.
* ppc-linux-nat.c (PTRACE_XFER_TYPE): Change the default for this
to 'long'.
(PPC_PTRACE_POKEUSR_3264, PPC_PTRACE_PEEKUSR_3264,
PPC_PTRACE_POKEDATA_3264, PPC_PTRACE_PEEKDATA_3264): Provide
default definitions for these.
(ARCH64): New macro.
(ppc_wordsize_pid): New function.
(kernel_u_size): Handle 64-bit case.
(ppc_register_u_addr): Same.
(fetch_register): Use the *_3264 requests when
debugging a 64-bit process from a 32-bit GDB.
(store_register): Same.
(GDB_MAX_ALLOCA, child_xfer_memory, udot_info): Copied from
infptrace.c.
(_initialize_ppc_linux_nat): New function, to register our copy of
the udot_info command.
* ppc-linux-tdep.c (TDEP): New macro.
(ppc64_linux_svr4_fetch_link_map_offsets): New function.
(read_memory_addr): Copied from rs6000-tdep.c.
(ppc64_linux_convert_from_func_ptr_addr): New function.
* rs6000-tdep.c (skip_prologue): Recognize more instructions for
saving the 'lr' and 'cr' registers; don't just pre-emptively mask
in the 'st' opcode as soon as we see an 'mflr' or 'mfcr' opcode.
Recognize more instructions for updating the stack pointer, and
loading the TOC pointer.
(registers_powerpc64, registers_a35): New register tables.
(rs6000_gdbarch_init): Register the 64-bit solib functions.
* solib-svr4.c (solib_break_names): If SOLIB_BREAK_NAME is
#defined, include an entry for it.
(enable_break): Call CONVERT_FROM_FUNC_PTR_ADDR when trying to
guess the linker's base address.
* config/powerpc/tm-linux.h
(ppc64_linux_svr4_fetch_link_map_offsets,
ppc64_linux_convert_from_func_ptr_addr): New declarations.