jit: implement gcc_jit_function_get_address

jit: implement gcc_jit_function_get_address

gcc/jit/ChangeLog:
	* docs/cp/topics/expressions.rst (Function pointers): New section.
	* docs/topics/compatibility.rst (LIBGCCJIT_ABI_9): New tag.
	* docs/topics/expressions.rst (Function pointers): New section.
	* docs/_build/texinfo/libgccjit.texi: Regenerate.
	* jit-common.h (class gcc::jit::recording::function_pointer): New
	forward decl.
	* jit-playback.c (gcc::jit::playback::function::get_address): New
	method.
	* jit-playback.h (gcc::jit::playback::function::get_address): New
	method decl.
	* jit-recording.c: Within namespace gcc::jit::recording...
	(function::function): Initialize new field "m_fn_ptr_type".
	(function::get_address): New method.
	(function_pointer::replay_into): New method.
	(function_pointer::visit_children): New method.
	(function_pointer::make_debug_string): New method.
	(function_pointer::write_reproducer): New method.
	* jit-recording.h: Within namespace gcc::jit::recording...
	(function::get_address): New method.
	(function): Add field "m_fn_ptr_type".
	(class function_pointer): New subclass of rvalue.
	* libgccjit++.h (gccjit::function::get_address): New method.
	* libgccjit.c (gcc_jit_function_get_address): New function.
	* libgccjit.h (LIBGCCJIT_HAVE_gcc_jit_function_get_address): New
	macro.
	(gcc_jit_function_get_address): New API entrypoint.
	* libgccjit.map (LIBGCCJIT_ABI_9): New tag.

gcc/testsuite/ChangeLog:
	* jit.dg/all-non-failing-tests.h: Add
	test-returning-function-ptr.c.
	* jit.dg/test-returning-function-ptr.c: New test case.

From-SVN: r253244