gdb: make gdbarch_make_corefile_notes return a unique ptr

gdb: make gdbarch_make_corefile_notes return a unique ptr

This patch starts by making the gdbarch_make_corefile_notes function
return a gdb::unique_xmalloc_ptr<char> and takes care of the fallouts,
mostly in linux-tdep.c and fbsd-tdep.c.

The difficulty in these files is that they use the BFD API for writing
core files, where you pass in a pointer to a malloc-ed buffer (or NULL
in the beginning), it re-allocs it if needed, and returns you the
possibly updated pointer.  I therefore used this pattern everywhere:

  note_data.reset (elfcore_write_note (obfd, note_data.release (), ...)

This hands over the ownership of note_data to the BFD function for the
duration of the call, and then puts its back in note_data right after
the call.

gdb/ChangeLog:

	* gdbarch.sh (make_corefile_notes): Return unique pointer.
	* gdbarch.c: Re-generate.
	* gdbarch.h: Re-generate.
	* gcore.c (write_gcore_file_1): Adjust.
	* fbsd-tdep.c (struct fbsd_collect_regset_section_cb_data): Add
	constructor.
	<note_data>: Change type to unique pointer.
	<abort_iteration>: Change type to bool.
	(fbsd_collect_regset_section_cb): Adjust to unique pointer.
	(fbsd_collect_thread_registers): Return void, adjust.
	(struct fbsd_corefile_thread_data): Add construtor.
	<note_data>: Change type to unique pointer.
	(fbsd_corefile_thread): Adjust.
	(fbsd_make_corefile_notes): Return unique pointer, adjust.
	* linux-tdep.c (linux_make_mappings_corefile_notes): Change type
	to unique pointer, adjust.
	(struct linux_collect_regset_section_cb_data): Add constructor.
	<note_data>: Change type to unique pointer.
	<abort_iteration>: Change type to bool.
	(linux_collect_thread_registers): Return void, adjust.
	(struct linux_corefile_thread_data): Add constructor.
	<note_data>: Change type to unique pointer.
	(linux_corefile_thread): Adjust.
	(linux_make_corefile_notes): Return unique pointer, adjust.

Change-Id: I1e03476bb47b87c6acb3e12204d193f38cc4e02b