Use go/types Selection in SelectorExpr
Remove old goroutine.go
Store unnamed results in funcs using defer
runtime, cmd/llgo: start implementing select

This is just part of the easy bit, constructing
the Select structure and registering cases.
runtime, cmd/llgo: implement most of select

Still to do:
 - synchronous sends (some strange compiler bug, generating
   invalid IR for what seems to be a simple couple of lines).
 - handling of nil channels
 - anything else I've forgotten
pkg/runtime: fix instruction domination

There's two problems here, one immediate one that
I've fixed; there was a variable declaration that
was being jumped over with a goto statement.

The obvious underlying problem is that the compiler
is not checking if variable declarations are being
jumped over.
Add a test for select statements