Fix CMake command line issue with EXPORT_NAME on Windows

[dcodeIO]

On Windows, if there's just cmd, the syntax -s 'EXPORT_NAME="Binaryen"' is invalid due to the single quotes.

shared:ERROR: Attempt to set a non-existent setting: ''EXPORT_NAME'
 - did you mean one of EXPORT_NAME, EXPORT_ES6, EXPORT_ALL?
 - perhaps a typo in emcc's  -s X=Y  notation?
 - (see src/settings.js for valid values)
ninja: build stopped: subcommand failed.

This removes the quotes, but I am not sure if this is still valid (on Linux). Perhaps CI will tell :)

[kripken]

Looks good, thanks!