compiler: fix interface lowering pass

It was removing some globals that still had uses left.

compiler/interface-lowering.go

@@ -440,12 +440,18 @@ func (p *lowerInterfacesPass) run() {
 	// numbers.
 	for _, typ := range p.types {
 		for _, use := range getUses(typ.typecode) {
-			if use.IsConstant() && use.Opcode() == llvm.PtrToInt {
+			if !use.IsAConstantExpr().IsNil() && use.Opcode() == llvm.PtrToInt {
 				use.ReplaceAllUsesWith(llvm.ConstInt(p.uintptrType, typ.num, false))
 			}
 		}
 	}
 
+	// Remove stray runtime.typeInInterface globals. Required for the following
+	// cleanup.
+	for _, global := range typesInInterfaces {
+		global.EraseFromParentAsGlobal()
+	}
+
 	// Remove method sets of types. Unnecessary, but cleans up the IR for
 	// inspection.
 	for _, typ := range p.types {