gccrs: Fix ICE in struct expressions

gccrs: Fix ICE in struct expressions

The error handling here was done long ago when we didnt know how to do
any error handling very well. This removed bad fatal_errors and adds in
some nice rich_location error diagnostics instead.

Fixes Rust-GCC#3628

gcc/rust/ChangeLog:

	* typecheck/rust-hir-type-check-struct-field.h: keep reference to parent expression
	* typecheck/rust-hir-type-check-struct.cc (TypeCheckStructExpr::TypeCheckStructExpr):
	update ctor
	(TypeCheckStructExpr::resolve): remove bad rust_fatal_errors
	(TypeCheckStructExpr::visit): cleanup errors

gcc/testsuite/ChangeLog:

	* rust/compile/macros/mbe/macro-issue2983_2984.rs: cleanup error diagnotics
	* rust/compile/struct_init1.rs: likewise
	* rust/compile/issue-3628.rs: New test.

Signed-off-by: Philip Herron <herron.philip@googlemail.com>