CMake sanitize alphanumeric string

To ensure created path names are compatible across computing platforms, it is useful to sanitize strings in general so that only alphanumeric characters are used to avoid adverse or accidental use of confusable UTF8 characters. In CMake this is accomplished like:

set(sneaky "âēĢ𝐚𝗅ð‘Ķ paly")
string(MAKE_C_IDENTIFIER ${sneaky} c)

message(NOTICE ${c})
# notice first characters and space are all underscore