gccrs: Fix ICE during const expr eval on array expressions

gccrs: Fix ICE during const expr eval on array expressions

Array expressions are still getting turned into VIEW_CONVERT_EXPR's becuase
TYPE_MAIN_VARIANT is not set so then we might as well reuse the type-hasher
to sort this out.

Fixes Rust-GCC#3588

gcc/rust/ChangeLog:

	* backend/rust-compile-context.h: only push named types
	* backend/rust-compile-type.cc (TyTyResolveCompile::visit): run the type hasher

gcc/testsuite/ChangeLog:

	* rust/compile/issue-3588.rs: New test.

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