muslc compat: support system without termios2

[GitMensch]

see removal in https://github.com/bminor/musl/commit/6fce6ca129c34d8975f777216d32cf92e77c18f2

Fixing the related parts seen in the build log for #4009.

[rocallahan]

Why are you putting these behind #ifdef TCGETS2? The ioctl exists and should be handled whether the C library defines this or not.

[GitMensch]

The libc does not have support for termios2, so that was the most easy way.
But as the kernel functions may still be called, it could be reasonable to define termios2 and the macros instead (to what exactly?).

If you leave some pointers I'll replace this PR by a change of this.

[rocallahan]

Add what you need to kernel_supplement.h.