[IRBuilder] Change the `gc.statepoint` creation interface

This is to enable me to address review for D13491 -- `Flags` is a
bitfield of `StatepointFlags`, not an individual item out of the enum,
so it should be represented as an `uint32_t`.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@249778 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed