c: Don't emit DEBUG_BEGIN_STMTs for K&R function argument declarations [PR105972]

c: Don't emit DEBUG_BEGIN_STMTs for K&R function argument declarations [PR105972]

K&R function parameter declarations are handled by calling
recursively c_parser_declaration_or_fndef in a loop, where each such
call will add_debug_begin_stmt at the start.
Now, if the K&R function definition is not a nested function,
building_stmt_list_p () is false and so we don't emit the DEBUG_BEGIN_STMTs
anywhere, but if it is a nested function, we emit it in the containing
function at the point of the nested function definition.
As the following testcase shows, it can cause ICEs if the containing
function has var-tracking disabled but nested function has them enabled,
as the DEBUG_BEGIN_STMTs are added to the containing function which
shouldn't have them but MAY_HAVE_DEBUG_MARKER_STMTS is checked already
for the nested function, or just wrong experience in the debugger.

The following patch ensures we don't emit any such DEBUG_BEGIN_STMTs for the
K&R function parameter declarations even in nested functions.

2023-01-11  Jakub Jelinek  <jakub@redhat.com>

	PR c/105972
	* c-parser.cc (c_parser_declaration_or_fndef): Disable debug non-bind
	markers for K&R function parameter declarations of nested functions.

	* gcc.dg/pr105972.c: New test.