Convert DTrace probe interface to C++ (and perform some cleanups)

Convert DTrace probe interface to C++ (and perform some cleanups)

This patch converts the DTrace probe
interface (gdb/dtrace-probe.[ch]) to C++, and also performs some
cleanups that were on my TODO list for a while.

The main changes were the conversion of 'struct dtrace_probe' to 'class
dtrace_probe', and a new 'class dtrace_static_probe_ops' to replace the
use of 'dtrace_probe_ops'.  Both classes implement the virtual methods
exported by their parents, 'class probe' and 'class static_probe_ops',
respectively.  I believe it's now a bit simpler to understand the
logic behind the dtrace-probe interface.

There are several helper functions used to parse parts of a dtrace
probe, and since they are generic and don't need to know about the
probe they're working on, I decided to leave them as simple static
functions (instead of e.g. converting them to class methods).

I've also converted a few uses of "VEC" to "std::vector", which makes
the code simpler and easier to maintain.  And, as usual, some cleanups
here and there.

Even though I'm sending a series of patches, they need to be tested
and committed as a single unit, because of inter-dependencies.  But it
should be easier to review in separate logical units.

I wasn't able to test these modifications because the current test
framework for DTrace probes is not working.  See
<https://sourceware.org/bugzilla/show_bug.cgi?id=22420>.

gdb/ChangeLog:
2017-11-22  Sergio Durigan Junior  <sergiodj@redhat.com>

	* dtrace-probe.c (struct probe_ops dtrace_probe_ops): Delete.
	(struct dtrace_probe_arg) <dtrace_probe_arg>: New constructor.
	<type_str>: Convert to 'std::string'.
	<expr>: Convert to 'expression_up'.
	(dtrace_probe_arg_s): Delete type and VEC.
	(dtrace_probe_enabler_s): Likewise.
	(struct dtrace_probe): Replace by...
	(class dtrace_static_probe_ops): ...this and...
	(class dtrace_probe): ...this.
	(dtrace_probe_is_linespec): Rename to...
	(dtrace_static_probe_ops::is_linespec): ...this.  Adjust code
	to reflect change.
	(dtrace_process_dof_probe): Use 'std::vector' instead of VEC.
	Adjust code.  Create new instance of 'dtrace_probe'.
	(dtrace_build_arg_exprs): Rename to...
	(dtrace_probe::build_arg_exprs): ...this.  Adjust code to
	reflect change.
	(dtrace_get_probes): Rename to...
	(dtrace_static_probe_ops::get_probes): ...this.  Adjust code
	to reflect change.
	(dtrace_get_arg): Rename to...
	(dtrace_probe::get_arg_by_number): ...this.  Adjust code to
	reflect change.
	(dtrace_probe_is_enabled): Rename to...
	(dtrace_probe::is_enabled): ...this.  Adjust code to reflect
	change.
	(dtrace_get_probe_address): Rename to...
	(dtrace_probe::get_relocated_address): ...this.  Adjust code
	to reflect change.
	(dtrace_get_probe_argument_count): Rename to...
	(dtrace_probe::get_argument_count): ...this.  Adjust code to
	reflect change.
	(dtrace_can_evaluate_probe_arguments): Rename to...
	(dtrace_probe::can_evaluate_arguments): ...this.  Adjust code
	to reflect change.
	(dtrace_evaluate_probe_argument): Rename to...
	(dtrace_probe::evaluate_argument): ...this.  Adjust code to
	reflect change.
	(dtrace_compile_to_ax): Rename to...
	(dtrace_probe::compile_to_ax): ...this.  Adjust code to
	reflect change.
	(dtrace_probe_destroy): Delete.
	(dtrace_type_name): Rename to...
	(dtrace_static_probe_ops::type_name): ...this.  Adjust code to
	reflect change.
	(dtrace_probe::get_static_ops): New method.
	(dtrace_gen_info_probes_table_header): Rename to...
	(dtrace_static_probe_ops::gen_info_probes_table_header):
	...this.  Adjust code to reflect change.
	(dtrace_gen_info_probes_table_values): Rename to...
	(dtrace_probe::gen_info_probes_table_values): ...this.  Adjust
	code to reflect change.
	(dtrace_enable_probe): Rename to...
	(dtrace_probe::enable_probe): ...this.  Adjust code to reflect
	change.
	(dtrace_disable_probe): Rename to...
	(dtrace_probe::disable_probe): ...this.  Adjust code to reflect
	change.
	(struct probe_ops dtrace_probe_ops): Delete.
	(info_probes_dtrace_command): Call 'info_probes_for_spops'
	instead of 'info_probes_for_ops'.
	(_initialize_dtrace_probe): Use 'all_static_probe_ops' instead
	of 'all_probe_ops'.