compiler: correctly generate code for local named types

It is possible to create function-local named types:

    func foo() any {
        type named int
        return named(0)
    }

This patch makes sure they don't alias with named types declared at the
package scope.

Bug originally found by Damian Gryski while working on reflect support.

compiler/compiler.go

@@ -71,6 +71,7 @@ type compilerContext struct {
 	difiles          map[string]llvm.Metadata
 	ditypes          map[types.Type]llvm.Metadata
 	llvmTypes        typeutil.Map
+	interfaceTypes   typeutil.Map
 	machine          llvm.TargetMachine
 	targetData       llvm.TargetData
 	intType          llvm.Type