interp: fix spurious variable declaration loop

The variable dependency check function was confused by a dependency
variable with the same name but in an external package.

This change is necessary to address #1427.

_test/p4/p4.go

@@ -0,0 +1,3 @@
+package p4
+
+var Value1 = "value1"

_test/p5.go

@@ -0,0 +1,10 @@
+package main
+
+import "github.com/traefik/yaegi/_test/p5"
+
+func main() {
+	println(*p5.Value1)
+}
+
+// Output:
+// value1

_test/p5/p5.go

@@ -0,0 +1,8 @@
+package p5
+
+import "github.com/traefik/yaegi/_test/p4"
+
+var (
+	Value1 = &val1
+	val1   = p4.Value1
+)

interp/cfg.go

@@ -2420,15 +2420,22 @@ func genGlobalVarDecl(nodes []*node, sc *scope) (*node, error) {
 
 func getVarDependencies(nod *node, sc *scope) (deps []*node) {
 	nod.Walk(func(n *node) bool {
-		if n.kind == identExpr {
-			if sym, _, ok := sc.lookup(n.ident); ok {
-				if sym.kind != varSym || !sym.global || sym.node == nod {
-					return false
-				}
-				deps = append(deps, sym.node)
-			}
+		if n.kind != identExpr {
+			return true
 		}
-		return true
+		// Process ident nodes, and avoid false dependencies.
+		if n.anc.kind == selectorExpr && childPos(n) == 1 {
+			return false
+		}
+		sym, _, ok := sc.lookup(n.ident)
+		if !ok {
+			return false
+		}
+		if sym.kind != varSym || !sym.global || sym.node == nod {
+			return false
+		}
+		deps = append(deps, sym.node)
+		return false
 	}, nil)
 	return deps
 }