DMD no longer requires libstdc++

[Seb]

Just a note for all DMD distro packagers out there that the DMD 
compiler no longer needs libstdc++ for building nor running.

However, of course as there are C++ ABI tests, it's still 
required for running the testsuite.

There are still a handful of CXX files in the DMD codebase, but 
once they have been converted to D too, the dependency on a host 
C++ compiler for building DMD can be entirely removed.


Details: https://github.com/dlang/dmd/pull/9188