cmd/compile: sort named types before unnamed in reflect

When the local package has an explicit name instead of "",
this is necessary to get past a cgo plugin test that fails
because of a package signature mismatch.  There's something
questionable going on in the package hash generation, and
in particular it went wrong here.  Updating the sort order
helps.

This CL is a prerequisite for a pending code cleanup,
https://go-review.googlesource.com/c/go/+/393715

Updates #51734.

The failure:

GOROOT/misc/cgo/testplugin$ go test .
mkdir -p $TMPDIR/src/testplugin
rsync -a testdata/ $TMPDIR/src/testplugin
echo 'module testplugin' > $TMPDIR/src/testplugin/go.mod
mkdir -p $TMPDIR/alt/src/testplugin
rsync -a altpath/testdata/ $TMPDIR/alt/src/testplugin
echo 'module testplugin' > $TMPDIR/alt/src/testplugin/go.mod
cd $TMPDIR/alt/src/testplugin
( PWD=$TMPDIR/alt/src/testplugin GOPATH=$TMPDIR/alt go build -gcflags '' -buildmode=plugin -o $TMPDIR/src/testplugin/plugin-mismatch.so ./plugin-mismatch )
cd $TMPDIR/src/testplugin
( PWD=$TMPDIR/src/testplugin GOPATH=$TMPDIR LD_LIBRARY_PATH=$TMPDIR/src/testplugin go build -gcflags '' -buildmode=plugin ./plugin1 )
( PWD=$TMPDIR/src/testplugin GOPATH=$TMPDIR LD_LIBRARY_PATH=$TMPDIR/src/testplugin go build -gcflags '' -buildmode=plugin ./plugin2 )
cp plugin2.so plugin2-dup.so
( PWD=$TMPDIR/src/testplugin GOPATH=$TMPDIR LD_LIBRARY_PATH=$TMPDIR/src/testplugin go build -gcflags '' -buildmode=plugin -o=sub/plugin1.so ./sub/plugin1 )
( PWD=$TMPDIR/src/testplugin GOPATH=$TMPDIR LD_LIBRARY_PATH=$TMPDIR/src/testplugin go build -gcflags '' -buildmode=plugin -o=unnamed1.so ./unnamed1/main.go )
( PWD=$TMPDIR/src/testplugin GOPATH=$TMPDIR LD_LIBRARY_PATH=$TMPDIR/src/testplugin go build -gcflags '' -buildmode=plugin -o=unnamed2.so ./unnamed2/main.go )
( PWD=$TMPDIR/src/testplugin GOPATH=$TMPDIR LD_LIBRARY_PATH=$TMPDIR/src/testplugin go build -gcflags '' -o host.exe ./host )
( PWD=$TMPDIR/src/testplugin GOPATH=$TMPDIR LD_LIBRARY_PATH=$TMPDIR/src/testplugin go run -gcflags '' ./checkdwarf/main.go plugin2.so plugin2.UnexportedNameReuse )
( PWD=$TMPDIR/src/testplugin GOPATH=$TMPDIR LD_LIBRARY_PATH=$TMPDIR/src/testplugin go run -gcflags '' ./checkdwarf/main.go ./host.exe main.main )
( PWD=$TMPDIR/src/testplugin GOPATH=$TMPDIR LD_LIBRARY_PATH=$TMPDIR/src/testplugin ./host.exe )
--- FAIL: TestRunHost (0.02s)
    plugin_test.go:187: ./host.exe: exit status 1
        2022/05/13 11:26:37 plugin.Open failed: plugin.Open("plugin1"): plugin was built with a different version of package runtime

and many more after that.

Change-Id: I0780decc5bedeea640ed0b3710867aeda5b3f725
Reviewed-on: https://go-review.googlesource.com/c/go/+/405995
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

src/cmd/compile/internal/reflectdata/reflect.go

@@ -1444,6 +1444,14 @@ type typesByString []typeAndStr
 
 func (a typesByString) Len() int { return len(a) }
 func (a typesByString) Less(i, j int) bool {
+	// put named types before unnamed types
+	if a[i].t.Sym() != nil && a[j].t.Sym() == nil {
+		return true
+	}
+	if a[i].t.Sym() == nil && a[j].t.Sym() != nil {
+		return false
+	}
+
 	if a[i].short != a[j].short {
 		return a[i].short < a[j].short
 	}