Guile: temporary breakpoints

Guile: temporary breakpoints

Adds API to the Guile bindings for creating temporary breakpoints and
querying whether an existing breakpoint object is temporary. This is
effectively a transliteration of the Python implementation.

It's worth noting that the added `is_temporary' flag is ignored in the
watchpoint registration path. This replicates the behaviour of the
Python implementation, but might be a bit surprising for users.

gdb/ChangeLog:

2021-06-09  George Barrett  <bob@bob131.so>

	* guile/scm-breakpoint.c (gdbscm_breakpoint_object::spec): Add
	is_temporary field.
	(temporary_keyword): Add keyword object for make-breakpoint
	argument parsing.
	(gdbscm_make_breakpoint): Accept #:temporary keyword argument
	and store the value in the allocated object's
	spec.is_temporary.
	(gdbscm_register_breakpoint_x): Pass the breakpoint's
	spec.is_temporary value to create_breakpoint.
	(gdbscm_breakpoint_temporary): Add breakpoint-temporary?
	procedure implementation.
	(breakpoint_functions::make-breakpoint): Update documentation
	string and fix a typo.
	(breakpoint_functions::breakpoint-temporary?): Add
	breakpoint-temporary? procedure.
	(gdbscm_initialize_breakpoints): Initialise temporary_keyword
	variable.
	NEWS (Guile API): Mention new temporary breakpoints API.

gdb/doc/ChangeLog:

2021-06-09  George Barrett  <bob@bob131.so>

	* guile.texi (Breakpoints In Guile): Update make-breakpoint
	documentation to reflect new #:temporary argument.
	Add documentation for new breakpoint-temporary? procedure.

gdb/testsuite/ChangeLog:

2021-06-09  George Barrett  <bob@bob131.so>

	* gdb.guile/scm-breakpoint.exp: Add additional tests for
	temporary breakpoints.

Change-Id: I2de332ee7c256f5591d7141ab3ad50d31b871d17