THRIFT-4547: Swift crosstests (#2670)

Co-authored-by: Jiayu Liu <Jimexist@users.noreply.github.com>
diff --git a/test/Makefile.am b/test/Makefile.am
index 478fb2c..d5f1434 100644
--- a/test/Makefile.am
+++ b/test/Makefile.am
@@ -92,6 +92,11 @@
 PRECROSS_TARGET += precross-rs
 endif
 
+if WITH_SWIFT
+SUBDIRS += swift
+PRECROSS_TARGET += precross-swift
+endif
+
 #
 # generate html for ThriftTest.thrift AND validate it!
 #
@@ -133,6 +138,7 @@
 	py.twisted \
 	rb \
 	rs \
+	swift \
 	threads \
 	partial \
 	AnnotationTest.thrift \