<concepts> header + std::common_reference ported from VC++

[Jonathan Wakely]

On 10/09/19 08:50 +0000, sotrdg sotrdg wrote:
>Hello everyone.
>
>I have ported the <concepts> header from VC++. Please add this <concepts> header in gcc 10.0.
>
>https://bitbucket.org/ejsvifq_mabmip/gcc-concepts-header/src/master/

What license is the original code under?
Who is the author of that code? Do you have permission to contribute
it to GCC?

I'm guessing the answer is no. There is no way we can accept a
contribution like this. See https://gcc.gnu.org/contribute.html#legal
for more information.

Anyway, I already have an implementation of common_reference and
various parts of the <concepts> header ready to commmit. I'm busy
writing the tests still. I see proper tests are missing from your
repo.