Linux: Keep termios ioctl constants strictly internal

Undefine TCGETS, TCGETS2, and related ioctl constants in the installed
headers.  Extract the correct constants (using the kernel type
definitions) automatically from the UAPI headers.  The kernel
constants are available under KERNEL_* names during the glibc build,
computed using assembler constant extraction mechanism.

Alpha may have to use TCGETS instead of TCGETS2 because TCTGETS2
became available in Linux 4.20 only.  Introduce ARCH_TCGETS to make
this choice explict.

To support emulation on powerpc, glibc versions of the termios
constants are added to the emulation code in internal-ioctl.h.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

sysdeps/unix/sysv/linux/termios_arch.h

@@ -1,23 +0,0 @@
-/* Architectural parameters for Linux termios - generic version
-
-   Copyright (C) 1997-2025 Free Software Foundation, Inc.
-   This file is part of the GNU C Library.
-
-   The GNU C Library is free software; you can redistribute it and/or
-   modify it under the terms of the GNU Lesser General Public
-   License as published by the Free Software Foundation; either
-   version 2.1 of the License, or (at your option) any later version.
-
-   The GNU C Library is distributed in the hope that it will be useful,
-   but WITHOUT ANY WARRANTY; without even the implied warranty of
-   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
-   Lesser General Public License for more details.
-
-   You should have received a copy of the GNU Lesser General Public
-   License along with the GNU C Library; if not, see
-   <https://www.gnu.org/licenses/>.  */
-
-#define _TERMIOS2_NCCS 19
-#define _HAVE_TERMIOS2_C_CC_BEFORE_C_LINE 0
-
-#define _HAVE_STRUCT_OLD_TERMIOS 0