[Bug bootstrap/63933] Build stage1 with -O2 during bootstrap if host compiler is a recent gcc version

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63933

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
Btw, non-GCC host compilers use their default optimization setting which is
usually optimizing.  We're only pessimizing our own GCC here...