www/{*chromium,iridium}: restrict usage of preserve_most to clang 17

the preserve_most attribute usage < clang 17 is causing weird runtime
issues in v8 and this commit backports a v8 commit that disables the
usage of this attribute with such compilers

Approved by: rene (mentor)
Obtained from: https://chromium.googlesource.com/v8/v8/+/ab12885a59d86d43a624ffaf6d56ca0d34e8e8bb