Delete the LLDS->x86_64 asm backend.

No progress has been made on the LLDS->x86_64 backend since the initial work on
it and it is now more have a maintenance headache then anything else.

compiler/llds_to_x86_64.m:
compiler/llds_to_x86_64_out.m:
compiler/x86_64_instrs.m:
compiler/x86_64_out.m:
compiler/x86_64_regs.m:
	Delete these modules.

compiler/globals.m:
	Delete the x86_64 target type.

compiler/*.m:
	Conform to the above changes.
Improve consistency of error and warning messages.

Add two new format components to the error_util library: decl/1 and
pragma_decl/1.  These are converted into strings as follows:

   decl(<Decl>)        ==> `:- <Decl>'
   pragma_decl(<Decl>) ==> `:- pragma <Decl>'

The motivation for this change is that error messages about declarations
often contain text similar to:

    ... in `:- foo' declaration ...

At least that is what occurs most of the time; in some cases the `:-' part is
omitted, in other cases the quotes are omitted.  Using the new format
components makes these consistency problems less likely to occur.  The error
specs are also more concise as well.

This commit also addresses a number of other minor issues related to error.

compiler/error_util.m:
	Add the two new format components describe above.

	Use add_quotes/1 as a single point of control for how single quotes
	are added where possible in this module.

	Call unexpected/3 in preference to error/1.

compiler/goal_expr_to_goal.m;
	Quote the word 'else' when referring the 'else' part of a try goal
	in an error message.

compiler/hlds_out_util.m:
	Add an XXX comment about cons_ids being incorrectly quoted in
	error messages.

compiler/det_report.m:
	Pass the message description to report_determinism_problem/7 as a list
	of format_components rather than as a string.

compiler/make_hlds_warn.m:
	Capitalize the word "Warning" when it occurs at the beginning of a warning.

compiler/typecheck_errors.m:
compiler/modules.m:
	Fix problems I noticed during my previous change.

compiler/add_pragma.m:
compiler/add_type.m:
compiler/det_analysis.m:
compiler/make_hlds_passes.m:
compiler/modules.m:
compiler/oisu_check.m:
compiler/prog_io.m:
compiler/prog_io_mode_defn.m:
compiler/prog_io_mutable.m:
compiler/prog_io_pragma.m:
compiler/prog_io_sym_name.m:
compiler/term_constr_errors.m:
compiler/term_errors.m
compiler/termination.m:
compiler/typecheck_errors.m:
	Conform to the above changes.

tests/invalid/bad_finalise_decl.err_exp:
tests/invalid/bad_initialise_decl.err_exp:
tests/invalid/bad_mutable.err_exp:
tests/invalid/bug83.err_exp:
tests/invalid/ee_invalid.err_exp:
tests/invalid/foreign_enum_import.err_exp:
tests/invalid/foreign_enum_invalid.err_exp:
tests/invalid/foreign_type_missing.err_exp:
tests/invalid/hawkins_mm_fail_reset.err_exp:
tests/invalid/loopcheck.err_exp:
tests/invalid/nested_impl_in_int.err_exp:
tests/invalid/oisu_check_add_pragma_errors.err_exp:
tests/invalid/oisu_check_semantic_errors.err_exp:
tests/invalid/reserve_tag.err_exp:
tests/invalid/try_io_else.err_exp:
tests/warnings/foreign_term_invalid.exp:
tests/warnings/warn_return.exp*:
tests/warnings/warn_succ_ind.exp*:
	Update expected (error) outputs to conform to the above.