Fixed a VC++ issue related to bitmasks. As it turns out the compiler fills the...

Fixed a VC++ issue related to bitmasks. As it turns out the compiler fills the unused bits of the word a bitmask is stored in with '1' (or randomly, I can't tell, I've seen '1' so far only), which creates wrong results in certain cases.

Please review.

llvm-svn: 42061