hub image: trial adding cxx-compiler

[consideRatio]

I'll go ahead and trial adding this package as it may pre-configure some path configurations etc for the gcc compiler's linker ld, and by doing so perhaps solving a failure to install https://regreg.github.io/regreg/download.html that fails like...

x86_64-conda_cos6-linux-gnu-gcc -pthread -shared -Wl,-O2 -Wl,--sort-common -Wl,--as-needed -Wl,-z,relro -Wl,-z,now -Wl,-rpath,/srv/conda/envs/notebook/lib -L/srv/conda/envs/notebook/lib -Wl,-O2 -Wl,--sort-common -Wl,--as-needed -Wl,-z,relro -Wl,-z,now -Wl,-rpath,/srv/conda/envs/notebook/lib -L/srv/conda/envs/notebook/lib -Wl,-O2 -Wl,--sort-common -Wl,--as-needed -Wl,-z,relro -Wl,-z,now -Wl,--disable-new-dtags -Wl,--gc-sections -Wl,-rpath,/srv/conda/envs/notebook/lib -Wl,-rpath-link,/srv/conda/envs/notebook/lib -L/srv/conda/envs/notebook/lib -march=nocona -mtune=haswell -ftree-vectorize -fPIC -fstack-protector-strong -fno-plt -O2 -ffunction-sections -pipe -isystem /srv/conda/envs/notebook/include -DNDEBUG -D_FORTIFY_SOURCE=2 -O2 -isystem /srv/conda/envs/notebook/include build/temp.linux-x86_64-3.8/regreg/atoms/projl1_cython.o -o build/lib.linux-x86_64-3.8/regreg/atoms/projl1_cython.cpython-38-x86_64-linux-gnu.so
/srv/conda/envs/notebook/bin/../lib/gcc/x86_64-conda-linux-gnu/9.3.0/../../../../x86_64-conda-linux-gnu/bin/ld: cannot find -lgcc
/srv/conda/envs/notebook/bin/../lib/gcc/x86_64-conda-linux-gnu/9.3.0/../../../../x86_64-conda-linux-gnu/bin/ld: cannot find -lgcc
collect2: error: ld returned 1 exit status