Added support for csversion API to dotnet toolset.

src/tools/dotnet.lua

@@ -294,6 +294,10 @@
 			table.insert(flags, table.implode(cfg.defines, "/d:", "", " "))
 		end
 
+		if cfg.csversion ~= nil then
+			table.insert(flags, '/langversion:' .. cfg.csversion)
+		end
+
 		return table.join(flags, cfg.buildoptions)
 	end
 

tests/tools/test_dotnet.lua

@@ -44,3 +44,14 @@
 		prepare()
 		test.isequal("mcs", dotnet.gettoolname(cfg, "csc"))
 	end
+
+
+--
+-- Check support for the `csversion` API
+--
+
+function suite.flags_csversion()
+	prepare()
+	csversion "7.2"
+	test.contains({ "/langversion:7.2" }, dotnet.getflags(cfg))
+end