C++ify xml-syscall.c

C++ify xml-syscall.c

This patch C++ifies the structures in xml-syscall.c, by using
std::vector instead of VEC, and std::string instead of char*.
Using a unique_ptr in syscall_parse_xml allows to remove a cleanup.

Something that seems strange with the existing code, if you look at
syscalls_info_free_syscalls_desc and
syscalls_info_free_syscall_group_desc, they free the structure elements
(the strings and vectors), but they don't free the syscall_desc and
syscall_group_desc structure themselves.  I don't see anything freeing
those currently.  Any idea why?  According to the comment above
syscalls_info_free_syscall_group_desc, it kinda looks like it's on
purpose.  With this patch, those structures are deleted when the vector
that contains them gets deleted.

The only time I'm aware a syscalls_info structure gets deleted is in the
case the data directory changes during runtime, in init_syscalls_info.
If tried that use case (including under valgrind):

 (gdb) catch syscall
 (gdb) set data-directory another-data-directory
 (gdb) catch syscall

I confirmed that the syscalls_info structure got deleted and recreated,
and everything seemed fine.

Regtested on the buildbot.

gdb/ChangeLog:

	* xml-syscall.c (struct syscall_desc): Add constructor.
	<name>: Change type to std::string.
	(syscall_desc_up): New typedef.
	(syscall_desc_p): Remove typeder.
	(DEF_VEC_P(syscall_desc_p)): Remove.
	(struct syscall_group_desc): Add constructor.
	<name>: Change type to std::string.
	<syscalls>: Change type to std::vector.
	(syscall_group_desc_up): New typedef.
	(syscall_group_desc_p): Remove typedef.
	(DEF_VEC_P(syscall_group_desc_p)): Remove.
	(struct syscalls_info) <syscalls>: Change type to std::vector of
	unique_ptr.
	<groups>: Likewise.
	<my_gdb_datadir>: Change type to std::string.
	(syscalls_info_up): New typedef.
	(allocate_syscalls_info): Remove.
	(syscalls_info_free_syscalls_desc): Remove.
	(syscalls_info_free_syscall_group_desc): Remove.
	(free_syscalls_info): Remove.
	(make_cleanup_free_syscalls_info): Remove.
	(syscall_group_create_syscall_group_desc): Adjust.
	(syscall_group_add_syscall): Adjust.
	(syscall_create_syscall_desc): Adjust.
	(syscall_parse_xml): Adjust, use unique_ptr instead of cleanup.
	(init_syscalls_info): Adjust.
	(syscall_group_get_group_by_name): Adjust.
	(xml_get_syscall_number): Adjust.
	(xml_get_syscall_name): Adjust.
	(xml_list_of_syscalls): Adjust.
	(xml_list_syscalls_by_group): Adjust.
	(xml_list_of_groups): Adjust.