In a 1-quart saucepan, combine the sugar and water and heat, stirring occasionally, until the sugar has dissolved. Once the sugar has dissolved and the syrup is hot, remove from the heat and add the chopped cilantro to the pan. Allow the syrup to cool for 15 minutes, then strain the syrup through a fine-mesh sieve. Discard the solids. The syrup may be made up to 2 weeks in advance and refrigerated in an airtight container until ready to use.