clang packages in 22.04 have the wrong libstdc++-*-dev dependency

[Gilles Peskine]

Summary: clang packages depends on the wrong version libstdc++-*-dev, so C++ compilation with Clang doesn't work without an extra, hard-to-discover step.

Workaround: apt install libstdc++-12-dev

The clang packages in Ubuntu 22.04 jammy are unusable to compile a C++ program out of the box.

```
$ cat a.cpp
#include <cstddef>
int main() {}
$ g++ a.cpp
$ clang++ a.cpp
a.cpp:1:10: fatal error: 'cstddef' file not found
#include <cstddef>
         ^~~~~~~~~
1 error generated.
$ clang++ --version
Ubuntu clang version 14.0.0-1ubuntu1.1
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
$ ls -lA $(which clang++)
lrwxrwxrwx 1 root root 26 Apr 1 2022 /usr/bin/clang++ -> ../lib/llvm-14/bin/clang++
$ dpkg -s clang-14 | grep -e Version -e Depends
Version: 1:14.0.0-1ubuntu1.1
Depends: libc6 (>= 2.34), libclang-cpp14 (>= 1:14.0.0), libgcc-s1 (>= 3.0), libllvm14, libstdc++6 (>= 11), libstdc++-11-dev, libgcc-11-dev, libobjc-11-dev, libclang-common-14-dev (= 1:14.0.0-1ubuntu1.1), llvm-14-linker-tools (= 1:14.0.0-1ubuntu1.1), libclang1-14 (= 1:14.0.0-1ubuntu1.1), libc6-dev, binutils
```

The problem turns out to be that clang++ 14 wants libstdc++-12-dev, but declares a dependency on libstdc++-11-dev.

I filed this bug under clang-14 because that's the default clang, but I think all the other Clang versions in Ubuntu 22.04 are affected.

This has happened before with different versions (https://bugs.launchpad.net/ubuntu/+source/llvm-toolchain-10/+bug/1878881).

[Tianxing Yang (ytxmobile)]

Can confirm this.

OS: Ubuntu 22.04 LTS

Clang version:
```
Ubuntu clang version 14.0.0-1ubuntu1.1
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
```

C++ code example:

```c++
#include <iostream>

using std::cout;
using std::endl;

int main(int argc, char** argv) {
    cout << "Hello, world!" << endl;
    return 0;
}
```

Tried `clang++ -v main.cc`, and got this:

```
Ubuntu clang version 14.0.0-1ubuntu1.1
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/11
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/12
Selected GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/12
Candidate multilib: .;@m64
Selected multilib: .;@m64
 "/usr/lib/llvm-14/bin/clang" -cc1 -triple x86_64-pc-linux-gnu -emit-obj -mrelax-all --mrelax-relocations -disable-free -clear-ast-before-backend -disable-llvm-verifier -discard-value-names -main-file-name main-kmp.cc -mrelocation-model pic -pic-level 2 -pic-is-pie -mframe-pointer=all -fmath-errno -ffp-contract=on -fno-rounding-math -mconstructor-aliases -funwind-tables=2 -target-cpu x86-64 -tune-cpu generic -mllvm -treat-scalable-fixed-error-as-warning -debugger-tuning=gdb -v -fcoverage-compilation-dir=/home/tianxing/dev/algorithms/KMP -resource-dir /usr/lib/llvm-14/lib/clang/14.0.0 -internal-isystem /usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../include/c++ -internal-isystem /usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../include/c++/x86_64-linux-gnu -internal-isystem /usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../include/c++/backward -internal-isystem /usr/lib/llvm-14/lib/clang/14.0.0/include -internal-isystem /usr/local/include -internal-isystem /usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../x86_64-linux-gnu/include -internal-externc-isystem /usr/include/x86_64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -fdeprecated-macro -fdebug-compilation-dir=/home/tianxing/dev/algorithms/KMP -ferror-limit 19 -fgnuc-version=4.2.1 -fcxx-exceptions -fexceptions -fcolor-diagnostics -faddrsig -D__GCC_HAVE_DWARF2_CFI_ASM=1 -o /tmp/main-kmp-a7fd49.o -x c++ main-kmp.cc
clang -cc1 version 14.0.0 based upon LLVM 14.0.0 default target x86_64-pc-linux-gnu
ignoring nonexistent directory "/usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../include/c++/x86_64-linux-gnu"
ignoring nonexistent directory "/usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../include/c++/backward"
ignoring nonexistent directory "/usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../x86_64-linux-gnu/include"
ignoring nonexistent directory "/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../include/c++
 /usr/lib/llvm-14/lib/clang/14.0.0/include
 /usr/local/include
 /usr/include/x86_64-linux-gnu
 /usr/include
End of search list.
main.cc:1:10: fatal error: 'iostream' file not found
#include <iostream>
         ^~~~~~~~~~
1 error generated.
```

Looks like it explicitly wants libstdc++-12-dev header & library files.

[Bernd Schubert (aakef)]

Also happens here, but not on all systems. One difference between these systems is that gcc-12 is installed on those that fail, but not on that that work. But then installing gcc-12 does not fail such systems - I'm still not sure what the trigger actually is.