Fail hard if sed isn't found

now that the new SDK is required and supplies it.

win32/build/confutils.js

@@ -2880,7 +2880,9 @@ function toolset_setup_project_tools()
 	}
 
 	/* TODO throw error, ignore for now for BC. */
-	PATH_PROG('sed');
+	if (!PATH_PROG('sed')) {
+		ERROR('sed is required')
+	}
 
 	RE2C = PATH_PROG('re2c');
 	if (RE2C) {