restrict BitScanForward() to VS2005+
restrict BitScanForward() to VS2005+

suggested by @aqrit in #947

unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso