[LangRef] Clarify undefined behavior for function attributes.

Violating the invariants specified by attributes is undefined behavior.
Maybe we could use poison instead for some of the parameter attributes,
but I don't think it's worthwhile.

Differential Revision: https://reviews.llvm.org/D49041



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@337947 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed