Require "target datalayout" to be at the beginning of an IR file.

This will allow us to use the datalayout to disambiguate other
constructs in IR, like load alignment. Split off from D78403.

Differential Revision: https://reviews.llvm.org/D78413

GitOrigin-RevId: 9b9454af8a525f92a19cc0a568777bb7c599c4cb
1 file changed