x11-fonts/noto-sans-math: Add noto-sans-math 2.539

When text is rendered by a computer, sometimes characters are displayed as
"tofu". They are little boxes to indicate your device doesn't have a font to
display the text.

Google has been developing a font family called Noto, which aims to support all
languages with a harmonious look and feel. Noto is Google's answer to tofu. The
name noto is to convey the idea that Google's goal is to see no more "tofu".
Noto has multiple styles and weights, and is freely available to all. The
comprehensive set of fonts and tools used in our development is available in our
GitHub repositories.

This port provides the fonts set of Noto Sans Math.