libgccjit: Add support for setting the comment ident

gcc/jit/ChangeLog:

	* docs/topics/compatibility.rst (LIBGCCJIT_ABI_34): New ABI tag.
	* docs/topics/contexts.rst: Document gcc_jit_context_set_output_ident.
	* jit-playback.cc (set_output_ident): New method.
	* jit-playback.h (set_output_ident): New method.
	* jit-recording.cc (recording::context::set_output_ident,
	recording::output_ident::output_ident,
	recording::output_ident::~output_ident,
	recording::output_ident::replay_into,
	recording::output_ident::make_debug_string,
	recording::output_ident::write_reproducer): New methods.
	* jit-recording.h (class output_ident): New class.
	* libgccjit.cc (gcc_jit_context_set_output_ident): New function.
	* libgccjit.h (gcc_jit_context_set_output_ident): New function.
	* libgccjit.map: New function.

gcc/testsuite/ChangeLog:

	* jit.dg/all-non-failing-tests.h: New test.
	* jit.dg/test-output-ident.c: New test.