bootstrap: update known compilers

como: Comeau-not updated since 2008, unlikely to work with CMake

icc: discontinued/removed/replaced by icx https://www.intel.com/content/www/us/en/developer/articles/release-notes/intel-oneapi-toolkit-release-notes.html

icc: not for C++, put in 20 years ago, probably never used / worked

Ref: f57a7ba9
Backport: release
Topic-rename: bootstrap-known-compilers