compiler: fix a few crashes due to named types

There were a few cases left where a named type would cause a crash in
the compiler. While going through enough code would have found them
eventually, I specifically looked for the `Type().(` pattern: a Type()
call that is then used in a type assert. Most of those were indeed bugs,
although for some I couldn't come up with a reproducer so I left them
as-is.

testdata/channel.go

@@ -8,6 +8,8 @@ import (
 
 var wg sync.WaitGroup
 
+type intchan chan int
+
 func main() {
 	ch := make(chan int, 2)
 	ch <- 1
@@ -40,6 +42,15 @@ func main() {
 	_ = make(chan int, uint32(2))
 	_ = make(chan int, uint64(2))
 
+	// Test that named channels don't crash the compiler.
+	named := make(intchan, 1)
+	named <- 3
+	<-named
+	select {
+	case <-named:
+	default:
+	}
+
 	// Test bigger values
 	ch2 := make(chan complex128)
 	wg.Add(1)

testdata/coroutines.go

@@ -68,6 +68,8 @@ func main() {
 	m.Unlock()
 	println("done")
 
+	startSimpleFunc(emptyFunc)
+
 	time.Sleep(2 * time.Millisecond)
 }
 
@@ -100,6 +102,11 @@ func sleepFuncValue(fn func(int)) {
 	go fn(8)
 }
 
+func startSimpleFunc(fn simpleFunc) {
+	// Test that named function types don't crash the compiler.
+	go fn()
+}
+
 func nowait() {
 	println("non-blocking goroutine")
 }
@@ -115,3 +122,8 @@ func (i *myPrinter) Print() {
 	time.Sleep(time.Millisecond)
 	println("async interface method call")
 }
+
+type simpleFunc func()
+
+func emptyFunc() {
+}

testdata/slice.go

@@ -31,6 +31,7 @@ func main() {
 	assert(len(make([]int, makeUint32(2), makeUint32(3))) == 2)
 	assert(len(make([]int, makeUint64(2), makeUint64(3))) == 2)
 	assert(len(make([]int, makeUintptr(2), makeUintptr(3))) == 2)
+	assert(len(make([]int, makeMyUint8(2), makeMyUint8(3))) == 2)
 
 	// indexing into a slice with uncommon index types
 	assert(foo[int(2)] == 4)
@@ -131,6 +132,9 @@ func main() {
 	var named MySlice
 	assert(len(unnamed[:]) == 32)
 	assert(len(named[:]) == 32)
+	for _, c := range named {
+		assert(c == 0)
+	}
 }
 
 func printslice(name string, s []int) {
@@ -169,3 +173,4 @@ func makeUint16(x uint16) uint16    { return x }
 func makeUint32(x uint32) uint32    { return x }
 func makeUint64(x uint64) uint64    { return x }
 func makeUintptr(x uintptr) uintptr { return x }
+func makeMyUint8(x myUint8) myUint8 { return x }