add patch to LLVM 20.1.5 to better support CUDA 13 and Blackwell GPUs

[Thyre]

(created using eb --new-pr)

See also: #23940

Description from that PR:

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With the introduction of Blackwell, NVIDIA has changed their ELF. As LLVM wasn't prepared for these changes, the validity of offload images could not be verified anymore. Hence, any program with an offload image failed during execution, if offloading is mandatory.

This can be seen in llvm/llvm-project#148703 and the related LLVM discourse.
Programs will for example fail with an error message like:

omptarget error: Consult https://openmp.llvm.org/design/Runtimes.html for debugging options.
omptarget error: No images found compatible with the installed hardware. 

The program will then crash, e.g. with the following stack trace:

Using host libthread_db library "/usr/lib/x86_64-linux-gnu/libthread_db.so.1".
omptarget error: Consult https://openmp.llvm.org/design/Runtimes.html for debugging options.
omptarget error: No images found compatible with the installed hardware. 
Program received signal SIGSEGV, Segmentation fault.
0x00007ffff5286ccf in llvm::object::ELFObjectFileBase::getNVPTXCPUName() const () from /opt/EasyBuild/apps/software/LLVM/20.1.8-GCCcore-14.3.0/lib/libLLVM.so.20.1
(gdb) bt
#0  0x00007ffff5286ccf in llvm::object::ELFObjectFileBase::getNVPTXCPUName() const () from /opt/EasyBuild/apps/software/LLVM/20.1.8-GCCcore-14.3.0/lib/libLLVM.so.20.1
#1  0x00007ffff5286c53 in llvm::object::ELFObjectFileBase::tryGetCPUName() const () from /opt/EasyBuild/apps/software/LLVM/20.1.8-GCCcore-14.3.0/lib/libLLVM.so.20.1
#2  0x00007ffff7a9cca1 in handleTargetOutcome(bool, ident_t*) () from /opt/EasyBuild/apps/software/LLVM/20.1.8-GCCcore-14.3.0/lib/x86_64-unknown-linux-gnu/libomptarget.so.20.1
#3  0x00007ffff7a97f43 in checkDevice(long&, ident_t*) () from /opt/EasyBuild/apps/software/LLVM/20.1.8-GCCcore-14.3.0/lib/x86_64-unknown-linux-gnu/libomptarget.so.20.1
#4  0x00007ffff7a984e0 in void targetData<AsyncInfoTy>(ident_t*, long, int, void**, void**, long*, long*, void**, void**, int (*)(ident_t*, DeviceTy&, int, void**, void**, long*, long*, void**, void**, AsyncInfoTy&, bool), char const*, char const*) ()
   from /opt/EasyBuild/apps/software/LLVM/20.1.8-GCCcore-14.3.0/lib/x86_64-unknown-linux-gnu/libomptarget.so.20.1
#5  0x00007ffff7a980c4 in __tgt_target_data_begin_mapper () from /opt/EasyBuild/apps/software/LLVM/20.1.8-GCCcore-14.3.0/lib/x86_64-unknown-linux-gnu/libomptarget.so.20.1
#6  0x000055555555ae7f in main ()

While this only affected Blackwell GPUs, CUDA 13.0 brought these ELF changes to prior generations as well.
Building an offload code with CUDA 13 and any architecture, one can see the exact same error message. See also llvm/llvm-project#159088

A fix was implemented for LLVM 22 in llvm/llvm-project#159354, and backported to LLVM 21 in llvm/llvm-project#159451. This PR brings the changes to LLVM 20.1.8 as well. The patch was slightly altered to handle differences between LLVM 20 and 21, but this shouldn't affect the functionality itself. They might also cleanly apply to older LLVM versions, which needs to be verified.

[Thyre]

@boegelbot please test @ jsc-zen3-a100

[boegelbot]

@Thyre: Request for testing this PR well received on jsczen3l1.int.jsc-zen3.fz-juelich.de

PR test command 'if [[ develop != 'develop' ]]; then EB_BRANCH=develop ./easybuild_develop.sh 2> /dev/null 1>&2; EB_PREFIX=/home/boegelbot/easybuild/develop source init_env_easybuild_develop.sh; fi; EB_PR=24040 EB_ARGS= EB_CONTAINER= EB_REPO=easybuild-easyconfigs EB_BRANCH=develop /opt/software/slurm/bin/sbatch --job-name test_PR_24040 --ntasks=8 --partition=jsczen3g --gres=gpu:1 ~/boegelbot/eb_from_pr_upload_jsc-zen3.sh' executed!

• exit code: 0
• output:

Submitted batch job 8085

Test results coming soon (I hope)...

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Message to humans: this is just bookkeeping information for me,
it is of no use to you (unless you think I have a bug, which I don't).

[Micket]

lgtm

[boegelbot]

Test report by @boegelbot
SUCCESS
Build succeeded for 2 out of 2 (2 easyconfigs in total)
jsczen3g1.int.jsc-zen3.fz-juelich.de - Linux Rocky Linux 9.6, x86_64, AMD EPYC-Milan Processor (zen3), 1 x NVIDIA NVIDIA A100 80GB PCIe, 580.82.07, Python 3.9.21
See https://gist.github.com/boegelbot/baa7585e284b1bfd54dbde0a383e579f for a full test report.

[ocaisa]

Going in, thanks @Thyre