Externals Update, master branch (2020.04.20.)

Updated all projects to atlasexternals-2.0.64.

The list of changes wrt. atlasexternals-2.0.63 is (atlasexternals@2.0.63...2.0.64):

• Updated MCUtils to version 1.3.4 (ping @zmarshal);
• Fixed the (standalone) build of Boost on macOS Catalina (ping @krumnack);
• Updated Acts to version v0.22.00, and switched to picking it up from GitHub (ping @pagessin);
• Turned off the unit tests for onnxruntime, thereby fixing its Clang 9 build (ATLINFR-3493, ping @dbakshig).

As noted in the list, this is meant to fix ATLINFR-3493.