Implement target_emit_ops

Implement target_emit_ops

This patch implements compiling agent expressions to native code for
AArch64.  This allows us to compile conditions set on fast tracepoints.

The compiled function has the following prologue:

High *------------------------------------------------------*
     | LR                                                   |
     | FP                                                   | <- FP
     | x1  (ULONGEST *value)                                |
     | x0  (unsigned char *regs)                            |
Low  *------------------------------------------------------*

We save the function's argument on the stack as well as the return
address and the frame pointer.  We then set the current frame pointer to
point to the previous one.

The generated code for the expression will freely update the stack
pointer so we use the frame pointer to refer to `*value' and `*regs'.
`*value' needs to be accessed in the epilogue of the function, in order
to set it to whatever is on top of the stack.  `*regs' needs to be passed
down to the `gdb_agent_get_raw_reg' function with the `reg' operation.

gdb/gdbserver/ChangeLog:

	* linux-aarch64-low-.c: Include ax.h and tracepoint.h.
	(enum aarch64_opcodes) <RET>, <SUBS>, <AND>, <ORR>, <ORN>,
	<EOR>, <LSLV>, <LSRV>, <ASRV>, <SBFM>, <UBFM>, <CSINC>, <MUL>,
	<NOP>: New.
	(enum aarch64_condition_codes): New enum.
	(w0): New static global.
	(fp): Likewise.
	(lr): Likewise.
	(struct aarch64_memory_operand) <type>: New
	MEMORY_OPERAND_POSTINDEX type.
	(postindex_memory_operand): New helper function.
	(emit_ret): New function.
	(emit_load_store_pair): New function, factored out of emit_stp
	with support for MEMORY_OPERAND_POSTINDEX.
	(emit_stp): Rewrite using emit_load_store_pair.
	(emit_ldp): New function.
	(emit_load_store): Likewise.
	(emit_ldr): Mention post-index instruction in comment.
	(emit_ldrh): New function.
	(emit_ldrb): New function.
	(emit_ldrsw): Mention post-index instruction in comment.
	(emit_str): Likewise.
	(emit_subs): New function.
	(emit_cmp): Likewise.
	(emit_and): Likewise.
	(emit_orr): Likewise.
	(emit_orn): Likewise.
	(emit_eor): Likewise.
	(emit_mvn): Likewise.
	(emit_lslv): Likewise.
	(emit_lsrv): Likewise.
	(emit_asrv): Likewise.
	(emit_mul): Likewise.
	(emit_sbfm): Likewise.
	(emit_sbfx): Likewise.
	(emit_ubfm): Likewise.
	(emit_ubfx): Likewise.
	(emit_csinc): Likewise.
	(emit_cset): Likewise.
	(emit_nop): Likewise.
	(emit_ops_insns): New helper function.
	(emit_pop): Likewise.
	(emit_push): Likewise.
	(aarch64_emit_prologue): New function.
	(aarch64_emit_epilogue): Likewise.
	(aarch64_emit_add): Likewise.
	(aarch64_emit_sub): Likewise.
	(aarch64_emit_mul): Likewise.
	(aarch64_emit_lsh): Likewise.
	(aarch64_emit_rsh_signed): Likewise.
	(aarch64_emit_rsh_unsigned): Likewise.
	(aarch64_emit_ext): Likewise.
	(aarch64_emit_log_not): Likewise.
	(aarch64_emit_bit_and): Likewise.
	(aarch64_emit_bit_or): Likewise.
	(aarch64_emit_bit_xor): Likewise.
	(aarch64_emit_bit_not): Likewise.
	(aarch64_emit_equal): Likewise.
	(aarch64_emit_less_signed): Likewise.
	(aarch64_emit_less_unsigned): Likewise.
	(aarch64_emit_ref): Likewise.
	(aarch64_emit_if_goto): Likewise.
	(aarch64_emit_goto): Likewise.
	(aarch64_write_goto_address): Likewise.
	(aarch64_emit_const): Likewise.
	(aarch64_emit_call): Likewise.
	(aarch64_emit_reg): Likewise.
	(aarch64_emit_pop): Likewise.
	(aarch64_emit_stack_flush): Likewise.
	(aarch64_emit_zero_ext): Likewise.
	(aarch64_emit_swap): Likewise.
	(aarch64_emit_stack_adjust): Likewise.
	(aarch64_emit_int_call_1): Likewise.
	(aarch64_emit_void_call_2): Likewise.
	(aarch64_emit_eq_goto): Likewise.
	(aarch64_emit_ne_goto): Likewise.
	(aarch64_emit_lt_goto): Likewise.
	(aarch64_emit_le_goto): Likewise.
	(aarch64_emit_gt_goto): Likewise.
	(aarch64_emit_ge_got): Likewise.
	(aarch64_emit_ops_impl): New static global variable.
	(aarch64_emit_ops): New target function, return
	&aarch64_emit_ops_impl.
	(struct linux_target_ops): Install it.