Make enum ModRefInfo an enum class. Changes to ModRefInfo values should be done using inline wrappers.
This should prevent future bit-wise operations from being added, which can be more error-prone.
FunctionModRefLocation and FunctionModRefBehavior remain enums.
Changes needed to migrate code (out of tree, branches etc):
- Replace all bit-wise operations with the inline methods declared in "include/llvm/Analysis/AliasAnalysis.h" (example replacements in D40749).
- Replace all occurrences of "MRI_*" with "ModRefInfo::*".