[X86] Fix Windows `i1 zeroext` conventions to use i8 instead of i32

Both GCC and MSVC only look at the low byte of a boolean when it is
passed.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@328386 91177308-0d34-0410-b5e6-96231b3b80d8
9 files changed