fix clang build error: replace static const with static constexpr

[smuzaffar]

This should fix the link errors in 94X CLANG IBs
https://cmssdt.cern.ch/SDT/cgi-bin/showBuildLogs.py/slc6_amd64_gcc630/www/mon/9.4.CLANG-mon-23/CMSSW_9_4_CLANG_X_2017-09-11-2300

[cmsbuild]

The code-checks are being triggered in jenkins.

[cmsbuild]

+code-checks

Logs: https://cmssdt.cern.ch/SDT/code-checks/PR-20468/639

[cmsbuild]

A new Pull Request was created by @smuzaffar (Malik Shahzad Muzaffar) for master.

It involves the following packages:

DataFormats/L1TGlobal
Validation/HGCalValidation

@vazzolini, @kmaeshima, @dmitrijus, @cmsbuild, @rekovic, @vanbesien, @mulhearn can you please review it and eventually sign? Thanks.
@vandreev11, @sethzenz, @kpedro88, @lgray, @cseez, @bsunanda, @pfs this is something you requested to watch as well.
@davidlange6, @slava77 you are the release manager for this.

cms-bot commands are listed here

[smuzaffar]

please test

[cmsbuild]

The tests are being triggered in jenkins.
https://cmssdt.cern.ch/jenkins/job/ib-any-integration/22881/console Started: 2017/09/12 10:19

[cmsbuild]

+1
Tested at: bd8ff7d
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-20468/22881/summary.html

The following merge commits were also included on top of IB + this PR after doing git cms-merge-topic:
69441fc
You can see more details here:
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-20468/22881/git-log-recent-commits
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-20468/22881/git-merge-result

[cmsbuild]

Comparison job queued.

[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-20468/22881/summary.html

Comparison Summary:

• No significant changes to the logs found
• Reco comparison results: 0 differences found in the comparisons
• DQMHistoTests: Total files compared: 26
• DQMHistoTests: Total histograms compared: 2642440
• DQMHistoTests: Total failures: 208
• DQMHistoTests: Total nulls: 0
• DQMHistoTests: Total successes: 2642043
• DQMHistoTests: Total skipped: 189
• DQMHistoTests: Total Missing objects: 0
• Checked 107 log files, 14 edm output root files, 26 DQM output files

[dmitrijus]

+1

[davidlange6]

merge