c: Improve build_component_ref diagnostics [PR91134]

c: Improve build_component_ref diagnostics [PR91134]

On the following testcase (the first dg-error line) we emit a weird
diagnostics and even fixit on pointerpointer->member
where pointerpointer is pointer to pointer to struct and we say
'pointerpointer' is a pointer; did you mean to use '->'?
The first part is indeed true, but suggesting -> when the code already
does use -> is confusing.
The following patch adjusts callers so that they tell it if it is from
. parsing or from -> parsing and in the latter case suggests to dereference
the left operand instead by adding (* before it and ) after it (before ->).
Or would a suggestion to add [0] before -> be better?

2022-05-25  Jakub Jelinek  <jakub@redhat.com>

	PR c/91134
gcc/c/
	* c-tree.h (build_component_ref): Add ARROW_LOC location_t argument.
	* c-typeck.cc (build_component_ref): Likewise.  If DATUM is
	INDIRECT_REF and ARROW_LOC isn't UNKNOWN_LOCATION, print a different
	diagnostic and fixit hint if DATUM has pointer type.
	* c-parser.cc (c_parser_postfix_expression,
	c_parser_omp_variable_list): Adjust build_component_ref callers.
	* gimple-parser.cc (c_parser_gimple_postfix_expression_after_primary):
	Likewise.
gcc/objc/
	* objc-act.cc (objc_build_component_ref): Adjust build_component_ref
	caller.
gcc/testsuite/
	* gcc.dg/pr91134.c: New test.