ah, ok, mono already ships with pre-compiled C# compiler and libraries, so this is complete and the 'mcs' package is not really needed in addition to this

mono/mono.spec

@@ -25,7 +25,7 @@
 
 #   package information
 Name:         mono
-Summary:      Unix .NET Development Framework: Runtime
+Summary:      Unix .NET Development Framework
 URL:          http://www.go-mono.com/
 Vendor:       The Mono Project
 Packager:     The OpenPKG Project
@@ -54,9 +54,9 @@ AutoReqProv:  no
     The Mono project is an open source effort to create a free Unix
     implementation of the .NET Development Framework. This is the base
     package providing a Common Language Runtime (CLR) for the Common
-    Language Infrastructure (CLI) and a set of class libraries. The
-    runtime can be embedded into your application. It implements both
-    ADO.NET and ASP.NET.
+    Language Infrastructure (CLI), a C# Compiler and a set of class
+    libraries. The runtime can be embedded into your application. It
+    implements both ADO.NET and ASP.NET.
 
 %track
     prog mono = {