[libcxx-commits] [libcxx] [libc++][doc] Add warning about limitation of --fresh in boostrapping build (PR #65265)

[Will Hawkins via libcxx-commits]

hawkinsw wrote:

I hope that my lost time saves someone else! 

cc @ldionne @ericwf (based on `git-blame` -- sorry if I inaccurately tagged!). 

https://github.com/llvm/llvm-project/pull/65265