Externals Update, 21.2 branch (2021.11.10.)

Updated all projects to atlasexternals-1.0.79. The changes wrt. atlasexternals-1.0.76 are (atlasexternals@1.0.76...1.0.79):

• Added FindTheP8I.cmake to AtlasLCG;
• Updated onnxruntime to version 1.5.1.

It is the latter update that's relevant for 21.2. Pinging @mfenton, @afarbin, @whiteson, @jraine and @dbakshig.

Note that I don't use full-build for the CI, only full-unit-tests. I believe this should be enough (even too much) for this update...