Add <span> Header to libstdc++

[Ed Smith-Rowland]

Conor,

I am CCing the libstdc++ list to get more eyes on this.  We send 
libstdc++ patches to both libstdc++ and gcc-patches.

Do you have Copyright assignment to the FSF?  You'll want to start hat 
quickly if you don't have it.

I am looking over your patch for <span> and it looks like a good start.

For the main patch there are mostly style issues (see 
gcc.gnu.org/onlinedocs/libstdc++//manual/source_code_style.html)

The biggest thing might be the testsuite.  You'll want a 
libstdc++-v3/testsuite/23_containers/span directory.  Look in the 
sibling directories for how these things are structured.

Best regards,

Ed Smith-Rowland

OP: https://gcc.gnu.org/ml/gcc-patches/2018-09/msg01658.html