This port extends the existing i686 port to support x86_64 by reusing
existing code whenever it makes sense.
* gdb/amd64-gnu-tdep.c: Adds logic for handling signal frames and
position of amd64 registers in the different Hurd structs.
The signal code is very similar to i686, except the trampoline code
is adapted.
* gdb/config/i386/nm-i386gnu.h: renamed to gdb/config/i386/nm-x86-gnu.h
and adapt it for x86_64.
* gdb/config/i386/i386gnu.mn: renamed to gdb/config/i386/nm-x86-gnu.mn
and reuse it for x86_64.
* gdb/configure.host: recognize gnu64 as a host.
* gdb/configure.nat: recognize gnu64 host and update existing i386gnu to
reuse the new shared files.
* gdb/configure.tgt: recognize x86_64-*-gnu* triplet and use
amd64-gnu-tdep.c.
* gdb/i386-gnu-tdep.c: added i386_gnu_thread_state_reg_offset that is
copied from i386-gnu-nat.c. This makes it similar to amd64.
* gdb/i386-gnu-nat.c: rename it to x86-gnu-nat.c since we reuse this for
i386 and amd64. Updated REG_ADDR to use one of the structures. Added
VALID_REGISTER to make sure it's a register we can provide at this time
(not all of them are available in amd64). FLAGS_REGISTER is either rfl
or efl depending on the arch. Renamed functions and class from i386 to x86
whenever they can be reused.
Tested on Hurd x86_64 and i686.
