This patch implements the new gdbarch method gdbarch_gdb_signal_to_target.

This patch implements the new gdbarch method gdbarch_gdb_signal_to_target.
It will be used when one wants to convert between the internal GDB signal
representation (enum gdb_signal) and the target's representation.

The idea of this patch came from a chat between Pedro and I on IRC, plus
the discussion of my patches to add the new $_exitsignal convenience
variable:

	<http://sourceware.org/ml/gdb-patches/2013-06/msg00452.html>
	<http://sourceware.org/ml/gdb-patches/2013-06/msg00352.html>

What I did was to investigate, on the Linux kernel, which targets shared
the signal numbers definition with the generic definition, present at
<include/uapi/asm-generic/signal.h>.  For the record, I used linux-3.10-rc7
as the main source of information, always looking at
<arch/<ARCH_NAME>/include/uapi/asm/signal.h>.  For SIGRTMAX (which defaults
to _NSIG in most cases), I had to look at different signal-related
files, but most of them (except MIPS) were defined to 64 anyway.

Then, with all the differences in hand, I implemented the bits on each
target.

2013-08-09  Sergio Durigan Junior  <sergiodj@redhat.com>

	* linux-tdep.c: Define enum with generic signal numbers.
	(linux_gdb_signal_from_target): New function.
	(linux_gdb_signal_to_target): Likewise.
	(linux_init_abi): Set gdbarch_gdb_signal_{to,from}_target
	methods to the functions above.
	* linux-tdep.h (linux_gdb_signal_from_target): New prototype.
	(linux_gdb_signal_to_target): Likewise.
	* alpha-linux-tdep.c: Define new enum with signals different
	from generic Linux kernel.
	(alpha_linux_gdb_signal_from_target): New function.
	(alpha_linux_gdb_signal_to_target): Likewise.
	(alpha_linux_init_abi): Set gdbarch_gdb_signal_{to,from}_target
	with the functions mentioned above.
	* avr-tdep.c: Define enum with differences between Linux kernel
	and AVR signals.
	(avr_linux_gdb_signal_from_target): New function.
	(avr_linux_gdb_signal_to_target): Likewise.
	(avr_gdbarch_init): Set gdbarch_gdb_signal_{to,from}_target to
	the functions mentioned above.
	* sparc-linux-tdep.c: Define enum with differences between SPARC
	and generic Linux kernel signal numbers.
	(sparc32_linux_gdb_signal_from_target): New function.
	(sparc32_linux_gdb_signal_to_target): Likewise.
	(sparc32_linux_init_abi): Set gdbarch_gdb_signal_{to,from}_target
	to the functions defined above.
	* xtensa-linux-tdep.c: Define enum with differences between
	Xtensa and Linux kernel generic signals.
	(xtensa_linux_gdb_signal_from_target): New function.
	(xtensa_linux_gdb_signal_to_target): Likewise.
	(xtensa_linux_init_abi): Set gdbarch_gdb_signal_to_target
	to the functions defined above.
	* mips-linux-tdep.c: Define enum with differences between
	signals in MIPS and Linux kernel generic ones.
	(mips_gdb_signal_to_target): New function.
	(mips_gdb_signal_from_target): Redefine to use new enum, handle
	only different signals from the Linux kernel generic.
	(mips_linux_init_abi): Set gdbarch_gdb_signal_{to,from}_target
	the functions defined above.
	* mips-linux-tdep.h (enum mips_signals): Remove.