add enhancements for windows build

[joachimmetz]

• add option to skip build of xattr on Windows
  • extend disabled with operating system - Changed build disabled option to support platform #1212
• add option to define pre-build scripts for cryptography, python-snappy and yara-python
  • have l2tdevtools build openssl and snappy?
  • set LIB and INCLUDE as configuration?
  • use prep-wheel.bat or prep-wheel.ps1?