prefs: Add EVIL_LIBS to build to avoid problems with missing regex.h under mingw

prefs: Add EVIL_LIBS to build to avoid problems with missing regex.h under mingw

Thanks to Adrien Nader to pointing this out.

In the longer term we need to re-factor some parts of the elm build system to
better reflect a build under mingw to avoid spreading @EVIL_LIBS@ and such
everywhere. But for now this is a good fix

@fix