I also am receiving similar errors as and followed ALMOST all the suggestions Michael Sartain suggested (I didn’t try building with clang v11.0.1 and applying the patch) but am still not able to build UE4Editor v4.26. I was successfully building v4.25.
The v4.26 branch builds with v17_clang-10.0.1-centos7
$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 18.04.5 LTS
Release: 18.04 Codename: bionic
Memory: 32 GB
$ uname -a
Linux jarvis 5.4.0-70-generic #78~18.04.1-Ubuntu SMP Sat Mar 20 14:10:07 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux
I will try the build process with the newer version of clang and see how that goes.