[llvm] use same host triple as set by gcc

[smuzaffar]

For ppc64le gcc11 builds, gcc properly use host triple to powerpc64le-redhat-linux-gnu while llvm uses powerpc64le-unknown-linux-gnu which causes cmssw build to fail as llvm could not find gcc headers. This change should make sure that same host tripel is used by llvm and gcc

[smuzaffar]

please test

[cmsbuild]

A new Pull Request was created by @smuzaffar (Malik Shahzad Muzaffar) for branch IB/CMSSW_12_1_X/gcc11.

@smuzaffar, @iarspider, @ddaina can you please review it and eventually sign? Thanks.
@perrotta, @dpiparo, @qliphy you are the release manager for this.
cms-bot commands are listed here

[smuzaffar]

test parameters:

• addpkg = CondFormats,CondTools,CondCore

[smuzaffar]

please test

[cmsbuild]

+1

Summary: https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-f67364/19955/summary.html
COMMIT: 18c8fed
CMSSW: CMSSW_12_1_X_2021-10-25-1100/slc7_amd64_gcc11
User test area: For local testing, you can use /cvmfs/cms-ci.cern.ch/week0/cms-sw/cmsdist/7411/19955/install.sh to create a dev area with all the needed externals and cmssw changes.

The following merge commits were also included on top of IB + this PR after doing git cms-merge-topic:

• @cms-sw Move GeneratorInterface-ReggeGribovPartonMCInterface to github #7405
• @ddaina don't build cudnn on slc7_aarch64 #7409
• @cms-sw build tensorflow with correct ppc64le_build_flags #7402

You can see more details here:
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-f67364/19955/git-recent-commits.json
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-f67364/19955/git-merge-result

Comparison Summary

Summary:

• No significant changes to the logs found
• Reco comparison results: 12121 differences found in the comparisons
• DQMHistoTests: Total files compared: 41
• DQMHistoTests: Total histograms compared: 2797338
• DQMHistoTests: Total failures: 122567
• DQMHistoTests: Total nulls: 6
• DQMHistoTests: Total successes: 2674743
• DQMHistoTests: Total skipped: 22
• DQMHistoTests: Total Missing objects: 0
• DQMHistoSizes: Histogram memory added: 0.004 KiB( 40 files compared)
• DQMHistoSizes: changed ( 312.0 ): 0.004 KiB MessageLogger/Warnings
• Checked 173 log files, 37 edm output root files, 41 DQM output files
• TriggerResults: no differences found