gccrs: Expand expressions/types correctly in more contexts.

gccrs: Expand expressions/types correctly in more contexts.

Expressions are expanded in constant/static items, match expressions
and in parentheses now. Types are expanded in enum variants.

gcc/rust/ChangeLog:

	* expand/rust-expand-visitor.cc (ExpandVisitor::visit):
	Expand expressions in more contexts.
	* resolve/rust-early-name-resolver.cc (EarlyNameResolver::visit):
	Visit enum variants.

gcc/testsuite/ChangeLog:

	* rust/compile/macro54.rs: New test.
	* rust/compile/macro55.rs: New test.

Signed-off-by: Matthew Jasper <mjjasper1@gmail.com>