Handle ERROR_MARK in direct_abstract_declarator

Handle ERROR_MARK in direct_abstract_declarator

The gcc.dg/noncompile/pr79758.c testcase prints

pr79758.c:5:6: error: redefinition of 'fn1'
'error_mark' not supported by direct_abstract_declarator)'/home/rguenther/src/gcc3/gcc/testsuite/gcc.dg/noncompile/pr79758.c:4:6: note: previous definition of 'fn1' with type

which shows a) re-entry of pp_printf via pp_unsupported_tree and b) a
bogus diagnostic.  The following handles ERROR_MARK in
direct_abstract_declarator, yielding in the better

/home/rguenther/src/gcc3/gcc/testsuite/gcc.dg/noncompile/pr79758.c:5:6: error: redefinition of 'fn1'
/home/rguenther/src/gcc3/gcc/testsuite/gcc.dg/noncompile/pr79758.c:4:6: note: previous definition of 'fn1' with type 'void(<type-error>)'

but still maybe not perfect.

2021-03-04  Richard Biener  <rguenther@suse.de>

gcc/c-family/
	* c-pretty-print.c (c_pretty_printer::direct_abstract_declarator):
	Handle ERROR_MARK.