THRIFT-4547: Swift crosstests (#2670)

Co-authored-by: Jiayu Liu <Jimexist@users.noreply.github.com>
diff --git a/lib/swift/Makefile.am b/lib/swift/Makefile.am
index 6b88b06..6a6644a 100644
--- a/lib/swift/Makefile.am
+++ b/lib/swift/Makefile.am
@@ -30,7 +30,7 @@
 	rm -rf .build
 
 precross:
-	swift
+	swift build
 
 check-local:
 	swift test