Restrict only to architectures that the code claims to support:
Python/TargetTool/TargetTool.py: help="ARCHS is one of list: IA32, X64, ARM, AARCH64 or EBC, which replaces target.txt's TARGET_ARCH definition. To specify more archs, please repeat this option." Python/build/buildoptions.py: help="ARCHS is one of list: IA32, X64, ARM, AARCH64, RISCV64 or EBC, which overrides target.txt's TARGET_ARCH definition. To specify more archs, please repeat this option."
See also: BaseTools/Source/C/GNUmakefile.
Result from attempt on powerpc64:
Attempting to detect HOST_ARCH from 'uname -m': powerpc Could not detected HOST_ARCH from uname results
Approved by: portmgr (tier-2 blanket)