naming conflict in genwqe-user with glibc >=2.30

[ngothan]

the latest glibc (v2.30) and newer declares its own gettid() function (see [0]) and this creates a naming conflict in genwqe-user which has a function with the same name.

[0] https://sourceware.org/git/?p=glibc.git;a=commit;h=1d0fc213824eaa2a8f8c4385daaa698ee8fb7c92

I made a proposed patch which resolves this issue. You find it in my pull request.

As alternative we could rename the gettid to sys_gettid.