Add binary prebuilt tools needed for host gtests

Bug: 147817558
Test: check testcases directory after "m general-tests"
Change-Id: If33dfdc6b3ad4792918383bf1481369735007113
diff --git a/build/art.go b/build/art.go
index 8deea23..af2a5de 100644
--- a/build/art.go
+++ b/build/art.go
@@ -291,10 +291,11 @@
 	defer artTestMutex.Unlock()
 
 	if ctx.Os().Class == android.Host {
-		path := ctx.Path().ToMakePath().String()
-		parts := strings.Split(path, "/")
-		// Keep last two parts of the path (e.g. bin/dex2oat).
-		testcasesContent[strings.Join(parts[len(parts)-2:], "/")] = path
+		src := ctx.SrcPath().String()
+		path := strings.Split(ctx.Path().ToMakePath().String(), "/")
+		// Keep last two parts of the install path (e.g. bin/dex2oat).
+		dst := strings.Join(path[len(path)-2:], "/")
+		testcasesContent[dst] = src
 	}
 }