linux: Consolidate lxstat{64}

linux: Consolidate lxstat{64}

The LFS support is implemented on lxstat64.c, instead of lxstat.c for
64-bit architectures.  The xstat.c implements the non-LFS and it is
a no-op for !XSTAT_IS_XSTAT64.

The generic non-LFS implementation handles two cases:

  1. New kABIs which uses generic pre 64-bit time Linux ABI (csky and
     nios): it issues __NR_fstat64 with AT_SYMLINK_NOFOLLOW plus handles
     the possible overflow off st_ino, st_size, or st_blocks.  It only
     handles _STAT_VER_KERNEL.

  2. Old KABIs with old non-LFS support (arm, i386, hppa, m68k,
     microblaze, s390, sh, powerpc, and sparc32).  For _STAT_VER_KERNEL
     it issues __NR_lstat, otherwise it isseus __NR_lstat64 and convert
     to non-LFS stat struct and handle possible overflows on st_ino,
     st_size, or st_blocks.

Also non-LFS mips is an outlier and it has its own implementation since
_STAT_VER_LINUX requires a different conversion function (it uses the
kernel_stat as the syscall argument since its exported ABI is different
than the kernel one for both non-LFS and LFS implementation).

The generic LFS implementation handles multiple cases:

  1. XSTAT_IS_XSTAT64 being 1:

    1.1. Old 64-bit kABI (ia64, powerpc64*, s390x, sparc64, x86_64): it
         issues __NR_lstat for _STAT_VER_KERNEL or _STAT_VER_LINUX.

    1.2. Old 64-bit kABI with defines __NR_lstat64 instead of __NR_lstat
         (sparc64): it issues __NR_lstat for _STAT_VER_KERNEL or
         __NR_lstat64 and convert to struct stat64.

    1.3. New kABIs which uses generic 64-bit Linux ABI (aarch64 and
         riscv64): it issues __NR_newfstatat with AT_SYMLINK_NOFOLLOW
	 and only for _STAT_VER_KERNEL.

    1.4. New 32-bit kABIs with only 64-bit time_t support (arc and
         riscv32): it issues __NR_statx and covert to struct stat64.

  2. Old ABIs with XSTAT_IS_XSTAT64 being 0:

    2.1. New kABIs which uses generic pre 64-bit time Linux ABI (csky
	 and nios2): it issues __NR_fstatat64 for _STAT_VER_KERNEL.

    2.2. Old kABIs with old non-LFS support (arm, i386, hppa, m68k,
	 microblaze, s390, sh, mips32, powerpc32, and sparc32): it
	 issues __NR_lstat64.

Also, two special cases requires specific LFS implementations:

  1. alpha: it requires to handle _STAT_VER_KERNEL64 to issue
     __NR_lstat64 and use the kernel_stat with __NR_lstat otherwise.

  2. mips64: as for non-LFS implementation its ABIs differ from
     glibc exported one, which requires a specific conversion
     function to handle the kernel_stat.

Checked with a build for all affected ABIs. I also checked on x86_64,
i686, powerpc, powerpc64le, sparcv9, sparc64, s390, and s390x.

Reviewed-by: Lukasz Majewski <lukma@denx.de>