[Bug bootstrap/58572] [4.9 regression] make bootstrap-lean leads to installation failure (doing extra rebuilds and invoking system compiler)

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58572

--- Comment #8 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 32288
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=32288&action=edit
gcc49-pr58572.patch

That didn't work for some reason (tried that just manually, after make
bootstrap-lean did ln -sf {,prev-}x86_64-unknown-linux-gnu, but make install
still failed when using g++ which doesn't grok -Wnarrowing and -Wno-narrowing
(used a shell script wrapper around /usr/bin/g++ that rejected those options).

But this patch worked, apparently libstdc++-v3 headers already use #pragma GCC
system_header, so this patch shouldn't make a difference warning-wise, but it
makes a difference for -MMD.