Fix link error in CLANG IBs caused by static const uninit vars

[mrodozov]

change static const to static constexpr as it was causing link error in CLANG IBs
https://cmssdt.cern.ch/SDT/cgi-bin/buildlogs/slc6_amd64_gcc630/CMSSW_9_4_CLANG_X_2017-09-25-2300/EventFilter/L1TRawToDigi
due to that as static const the var might not get (and it's not) initialized

[cmsbuild]

The code-checks are being triggered in jenkins.

[cmsbuild]

+code-checks

Logs: https://cmssdt.cern.ch/SDT/code-checks/PR-20653/962

[mrodozov]

please test

[cmsbuild]

The tests are being triggered in jenkins.
https://cmssdt.cern.ch/jenkins/job/ib-any-integration/23225/console Started: 2017/09/26 12:12

[cmsbuild]

A new Pull Request was created by @mrodozov for master.

It involves the following packages:

DataFormats/L1Trigger
EventFilter/L1TRawToDigi

@cmsbuild, @rekovic, @mulhearn can you please review it and eventually sign? Thanks.
@Martin-Grunewald, @rovere, @kreczko, @thomreis this is something you requested to watch as well.
@davidlange6, @slava77 you are the release manager for this.

cms-bot commands are listed here

[cmsbuild]

+1
Tested at: 1d06afc
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-20653/23225/summary.html

The following merge commits were also included on top of IB + this PR after doing git cms-merge-topic:
239fbbd
You can see more details here:
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-20653/23225/git-log-recent-commits
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-20653/23225/git-merge-result

[cmsbuild]

Comparison job queued.

[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-20653/23225/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: 2691683
• DQMHistoTests: Total failures: 208
• DQMHistoTests: Total nulls: 0
• DQMHistoTests: Total successes: 2691286
• DQMHistoTests: Total skipped: 189
• DQMHistoTests: Total Missing objects: 0
• Checked 107 log files, 15 edm output root files, 26 DQM output files