cmd/api: work on Windows again, and make gccgo files work a bit more

handle string and []byte conversions.

R=golang-dev, dsymonds
CC=golang-dev
https://golang.org/cl/5754082

src/cmd/api/goapi.go

@@ -579,7 +579,14 @@ func (w *Walker) varValueType(vi interface{}) (string, error) {
 			}
 		}
 		// maybe a function call; maybe a conversion.  Need to lookup type.
-		return "", fmt.Errorf("not a known function %q", w.nodeString(v.Fun))
+		// TODO(bradfitz): this is a hack, but arguably most of this tool is,
+		// until the Go AST has type information.
+		nodeStr := w.nodeString(v.Fun)
+		switch nodeStr {
+		case "string", "[]byte":
+			return nodeStr, nil
+		}
+		return "", fmt.Errorf("not a known function %q", nodeStr)
 	default:
 		return "", fmt.Errorf("unknown const value type %T", vi)
 	}

src/cmd/api/testdata/src/pkg/p1/golden.txt

@@ -58,14 +58,16 @@ pkg p1, type T struct
 pkg p1, type TPtrExported struct
 pkg p1, type TPtrExported struct, embedded *Embedded
 pkg p1, type TPtrUnexported struct
+pkg p1, var ByteConv []byte
 pkg p1, var ChecksumError error
 pkg p1, var SIPtr *SI
 pkg p1, var SIPtr2 *SI
 pkg p1, var SIVal SI
+pkg p1, var StrConv string
 pkg p1, var V string
-pkg p1, var VError Error
 pkg p1, var V1 uint64
 pkg p1, var V2 p2.Twoer
+pkg p1, var VError Error
 pkg p1, var X I
 pkg p1, var X int64
 pkg p1, var Y int

src/cmd/api/testdata/src/pkg/p1/p1.go

@@ -27,6 +27,12 @@ var (
 	V2     = ptwo.G()
 )
 
+// Variables with conversions:
+var (
+	StrConv  = string("foo")
+	ByteConv = []byte("foo")
+)
+
 var ChecksumError = ptwo.NewError("gzip checksum error")
 
 const B = 2