jit: set DECL_CONTEXT of RESULT_DECL [PR103562]

libgccjit was failing to set the DECL_CONTEXT of function RESULT_DECLs,
leading to them failing to be properly handled by the inlining machinery.
Fixed thusly.

gcc/jit/ChangeLog:
	PR jit/103562
	* jit-playback.c (gcc::jit::playback::context::new_function): Set
	DECL_CONTEXT of the result_decl.

gcc/testsuite/ChangeLog:
	PR jit/103562
	* jit.dg/all-non-failing-tests.h: Add comment about...
	* jit.dg/test-pr103562.c: New test.

Signed-off-by: David Malcolm <dmalcolm@redhat.com>