[Cmake] regular expressions with special symbols

[Eric Wing]

I need to write a small macro which needs to check if
a file extension exists in a string, and if so, what
that extension is.

I would like to do some kind of check using something
like *.cpp, but the '.' is a special symbol. I tried
using a backslash to escape the symbol, but it didn't
seem to work.

Is there a different way to escape characters with
CMake?

Thanks,
Eric