ubuntu: add libstdc++-dev

[junghans]

This will hopefully fix:

2026-03-17T18:58:24.1551844Z -- Check for working CXX compiler: /usr/bin/clang++
2026-03-17T18:58:24.2217833Z CMake Error at /usr/share/cmake-4.2/Modules/CMakeTestCXXCompiler.cmake:73 (message):
2026-03-17T18:58:24.2218798Z -- Check for working CXX compiler: /usr/bin/clang++ - broken
2026-03-17T18:58:24.2220018Z   The C++ compiler
2026-03-17T18:58:24.2220263Z 
2026-03-17T18:58:24.2220411Z     "/usr/bin/clang++"
2026-03-17T18:58:24.2220606Z 
2026-03-17T18:58:24.2220746Z   is not able to compile a simple test program.
2026-03-17T18:58:24.2220990Z 
2026-03-17T18:58:24.2221203Z   It fails with the following output:
2026-03-17T18:58:24.2221447Z 
2026-03-17T18:58:24.2221721Z     Change Dir: '/__w/votca/votca/builddir/CMakeFiles/CMakeScratch/TryCompile-tXEhLh'
2026-03-17T18:58:24.2222187Z     
2026-03-17T18:58:24.2222437Z     Run Build Command(s): /usr/bin/ninja -v cmTC_040c3
2026-03-17T18:58:24.2223823Z     [1/2] /usr/bin/clang++    -MD -MT CMakeFiles/cmTC_040c3.dir/testCXXCompiler.cxx.o -MF CMakeFiles/cmTC_040c3.dir/testCXXCompiler.cxx.o.d -o CMakeFiles/cmTC_040c3.dir/testCXXCompiler.cxx.o -c /__w/votca/votca/builddir/CMakeFiles/CMakeScratch/TryCompile-tXEhLh/testCXXCompiler.cxx
2026-03-17T18:58:24.2225445Z     [2/2] : && /usr/bin/clang++   CMakeFiles/cmTC_040c3.dir/testCXXCompiler.cxx.o -o cmTC_040c3   && :
2026-03-17T18:58:24.2225975Z     FAILED: [code=1] cmTC_040c3 
2026-03-17T18:58:24.2226450Z     : && /usr/bin/clang++   CMakeFiles/cmTC_040c3.dir/testCXXCompiler.cxx.o -o cmTC_040c3   && :
2026-03-17T18:58:24.2227116Z     /usr/bin/x86_64-linux-gnu-ld.bfd: cannot find -lstdc++: No such file or directory
2026-03-17T18:58:24.2227744Z     clang++: error: linker command failed with exit code 1 (use -v to see invocation)
2026-03-17T18:58:24.2228240Z     ninja: build stopped: subcommand failed.