THRIFT-3906 Run C# tests with make check

This closes #1069
diff --git a/test/Makefile.am b/test/Makefile.am
index 1d52c59..fb39a12 100755
--- a/test/Makefile.am
+++ b/test/Makefile.am
@@ -25,6 +25,11 @@
 PRECROSS_TARGET += precross-c_glib
 endif
 
+if WITH_MONO
+SUBDIRS += csharp
+PRECROSS_TARGET += precross-csharp
+endif
+
 if WITH_CPP
 SUBDIRS += cpp
 PRECROSS_TARGET += precross-cpp