THRIFT-264. csharp: Use /langversion:linq to fix the Linux build


git-svn-id: https://svn.apache.org/repos/asf/incubator/thrift/trunk@740454 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/lib/csharp/Makefile.am b/lib/csharp/Makefile.am
index d96bef0..8395266 100644
--- a/lib/csharp/Makefile.am
+++ b/lib/csharp/Makefile.am
@@ -31,7 +31,7 @@
 all-local: Thrift.dll
 
 Thrift.dll: $(THRIFTCODE)
-	$(CSC) $(THRIFTCODE) /out:Thrift.dll /target:library
+	$(CSC) $(THRIFTCODE) /out:Thrift.dll /target:library /langversion:linq
 
 clean-local:
 	$(RM) Thrift.dll