fix OSX issue in VSO build

also, make it possible to have more verbose build runs when needed

scripts/dotnet-cli-build/Utils/EnvVars.cs

@@ -0,0 +1,32 @@
+using System;
+
+namespace Microsoft.DotNet.Cli.Build
+{
+    public class EnvVars
+    {
+        public static readonly bool Verbose = GetBool("DOTNET_BUILD_VERBOSE");
+
+        private static bool GetBool(string name, bool defaultValue = false)
+        {
+            var str = Environment.GetEnvironmentVariable(name);
+            if (string.IsNullOrEmpty(str))
+            {
+                return defaultValue;
+            }
+
+            switch (str.ToLowerInvariant())
+            {
+                case "true":
+                case "1":
+                case "yes":
+                    return true;
+                case "false":
+                case "0":
+                case "no":
+                    return false;
+                default:
+                    return defaultValue;
+            }
+        }
+    }
+}