Fix clang-tidy performance issues.

src/Bitrounding.cc

src/Detrend.cc

src/Diff.cc

src/EcaEtccdi.cc

src/EcaIndices.cc

src/Exprf.cc

src/Intlevel.cc

src/Select.cc

src/Selregion.cc

src/Setgridcell.cc

src/Smooth.cc

src/Trend.cc

src/Trendarith.cc

src/Vertstat.cc

src/Ydaystat.cc

src/cdo_apply.cc

src/cdo_output.cc

src/module_info.cc

src/module_info.h

src/modules.cc