jit: New API entrypoint: gcc_jit_context_get_last_error

jit: New API entrypoint: gcc_jit_context_get_last_error

gcc/jit/ChangeLog:
	* docs/topics/contexts.rst (Error-handling): Document new
	entrypoint gcc_jit_context_get_last_error.
	* docs/_build/texinfo/libgccjit.texi: Regenerate.
	* jit-recording.c (gcc::jit::recording::context::context):
	Initialize new fields "m_last_error_str" and
	"m_owns_last_error_str".
	(gcc::jit::recording::context::~context): Clean up
	m_last_error_str, if needed.
	(gcc::jit::recording::context::add_error_va): Update
	m_last_error_str and m_owns_last_error_str, freeing the old
	value if appropriate.
	(gcc::jit::recording::context::get_last_error): New function.
	* jit-recording.h (gcc::jit::recording::context::get_last_error):
	New function.
	(gcc::jit::recording::context): New fields m_last_error_str and
	m_owns_last_error_str.
	* libgccjit.c (gcc_jit_context_get_last_error): New function.
	* libgccjit.h (gcc_jit_context_get_last_error): New declaration.
	* libgccjit.map (gcc_jit_context_get_last_error): New function.

gcc/testsuite/ChangeLog:
	* jit.dg/test-error-block-in-wrong-function.c (verify_code):
	Verify the result of gcc_jit_context_get_last_error.
	* jit.dg/test-error-null-passed-to-api.c (verify_code): Likewise.

From-SVN: r219363