Update README.md

[benlaurie]

It seems that other packages installing odd versions of gcc can cause libstdc++ to be missing.

[jrtc27]

My guess is that:

1. You had gcc-12 installed (and possibly older gcc/g++ packages, likely -11), but not g++-12
2. Clang saw 12 as the newest GCC version
3. Clang used GCC 12's headers (it likes to use the newest version available)

burn:~ jrtc4% docker run --rm -it ubuntu:22.04
root@1b5489962837:/# apt update
...
root@1b5489962837:/# apt install -y gcc g++ clang
...
root@1b5489962837:/# echo '#include <new>' | clang++ -x c++ - -fsyntax-only
root@1b5489962837:/# apt install -y gcc-12
...
root@1b5489962837:/# echo '#include <new>' | clang++ -x c++ - -fsyntax-only
<stdin>:1:10: fatal error: 'new' file not found
#include <new>
         ^~~~~
1 error generated.

This documentation certainly isn't the right fix; libstdc++-12-dev is extremely specific to your situation. I don't think there's much we can really do here, unfortunately, this is a long-standing deficiency in Clang.

[jrtc27]

As above

[benlaurie]

OK, so I documented the issue instead.

[benlaurie]

Maybe we should fix clang?

[arichardson]

LGTM, @jrtc27 are you okay with the current wording?