CentOS 7 Fixes, 1.0.27-patches branch (2020.10.05.)

I created the 1.0.27-patches branch to be able to fix the build of the Athena-21.0-mc16a and Athena-21.0-mc16d branches for the x86_64-centos7-gcc62-opt platform. A more detailed discussion about this can be found in: ATLINFR-3741

I didn't have to write any new code in the end, I just cherry-picked everything that I deemed necessary, from the 1.0.48-patches branch. (Which is used by the the rest of the 21.X branches, excluding 21.2...)

The only worrisome point here is that 1.0.48-patches uses a newer version of yampl than what is in 1.0.27. But since this is a "technical external" that should not affect physics in any way, I decided to just update to the newer version. Instead of developing the correct patching setup for this branch separately.