OpenMP 5.2 deprecates the '-' reduction operator (-Wdeprecated-openmp)
because it is functionally identical to '+': the private reduction copy
is initialised to 0 and partial results are combined by addition in both
cases. All affected loops accumulate with 'mllh += ...', so switching to
reduction(+:mllh) is results-identical and silences the warning.
Fixes the pragma in PRunMuMinus.cpp and the two in PRunSingleHisto.cpp,
and corrects the now-inaccurate "for subtraction" doc comment.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
suter_a
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