Add support for abi-tags (adapted from Fedora's patch)

[ellert]

https://sft.its.cern.ch/jira/browse/ROOT-7818
https://sft.its.cern.ch/jira/browse/ROOT-7721
https://sft.its.cern.ch/jira/browse/ROOT-7654
https://sft.its.cern.ch/jira/browse/ROOT-7319
https://sft.its.cern.ch/jira/browse/ROOT-7285
Possibly more...

Adapted from:
http://pkgs.fedoraproject.org/cgit/llvm.git/tree/0001-add-gcc-abi_tag-support.patch

[Axel-Naumann]

Hi Mattias,

Thanks for collecting those. How does this PR relate to http://reviews.llvm.org/D12834 ?

Cheers, Axel

[ellert]

The Fedora patch and the llvm review are very much related. The Fedora patch is based on the proposed changes - there is a reference to http://reviews.llvm.org/D12834?id=34645 in the Fedora patch. Making a diff between the Fedora patch and the llvm review shows no significant changes (there are differences because the diffs are generated with different tools).

The proposed changes here differs because the patch must be adapted to the llvm version used by root.

[Axel-Naumann]

Hi Mattias,

Thanks for your PR! Here's the plan:

I will update llvm and clang still this month. Very likely that'll not be enough to give us GCC5 ABI support.

I will then take what's in D12834 and friends (there are a few follow-ups as far as I can see) and apply them for a round of tests. As long as it doesn't break GCC 4.9 we are better off than now.

Cheers, Axel.

[12345ieee]

Another bug report related to this issue:
https://sft.its.cern.ch/jira/browse/ROOT-7895

I confirm that after applying this patch (against 44c8e52) everything seems to work well.
Debian sid, gcc 5.3.1

Thanks @ellert .

[Axel-Naumann]

Hi,

I will import the current state of the patch under review with llvm / clang, instead of the original one proposed here. There have been significant changes since.

So yes - this will be dealt with (see also the open Jira tickets), but not exactly as proposed here.

Thanks anyway for the suggestion!

Cheers, Axel.