waf: defines: VDA/VDPAU/VAAPI/VAAPI_VPP
waf: add zlib check
waf: DEFINES: zlib
waf: DEFINES: stream cache
waf: fix stream cache compilation
waf: correctly define stuff on check_true
waf: fix cpudetect to use globals
waf: remove missing parens warnings
waf: dependencies: automatically detect OS
waf: refactor header generation