[llvm] [ARM] Recognize abi tag module flags (PR #161306)

[Peter Smith via llvm-commits]

https://github.com/smithp35 commented:

Just to make sure I understand. If there are no module flags for `arm-eabi-fp-exceptions`, `arm-eabi-fp-denormal` and `arm-eabi-fp-number-model` then the `mdconst::extract_or_null<ConstantInt>(MD... )` will return nullptr and we'll fall back to checking function attribute consistency.

How are the module flags expected to be set by the front-end? In particular are the module flags always set (with default values) if the user does not express a preference.

I'd like to make sure that the LTO case where the user doesn't put the floating point options on the command line for the final link step (with just objects) still works as it does today.

https://github.com/llvm/llvm-project/pull/161306