[Bug target/111570] -march=generic prints error

["brjd_epdjq36 at kygur dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111570

--- Comment #2 from Brjd <brjd_epdjq36 at kygur dot com> ---
Thank you and I also read this guide. My point is that the generic arch might
be  possible in theory. If the gcc builds for the oldest CPU with x86_64, is it
possible that code will run on all modern CPU since their subset includes also
that of their predecessor. 

How about making it default to that generic or baseline build for that limited
CPU?

If I could ask you also more questions, let me ask you about this problem. The
guide doesn't mention anything about the specific arch. If -march=cpu what is
better -mtune=cpu where cpu is the same as in arch or -mtune=generic so that
the code tunes to all CPU kinds of this family.If the tune is empty, is it
default generic or native and the arch is not clear either.

One question more, I am not able to find a guide about the gcc build and no
information whether the gcc may be built in targets like LLVM and clang. For
example, is it possible to build first only the LLVM, then stop and resume with
clang etc. or first, gcc's only c modiule and its submodules, then stop and
resume with its g++  module and submodules, next with libgcc, libstdc++ etc.? 

It would be great, especially for long bootstraps and stage 2, but I find only
make all-gcc, target-libgcc which however build almost all of the compiler.