Consolidate Linux getdents{64} implementation

Consolidate Linux getdents{64} implementation

This patch consolidates Linux getdents{64} implementation on just
the default sysdeps/unix/sysv/linux/getdents{64}{_r}.c ones.

Although this symbol is used only internally, the non-LFS version
still need to be build due the non-LFS getdirentries which requires
its semantic.

The non-LFS default implementation now uses the wordsize-32 as base
which uses getdents64 syscall plus adjustment for overflow (it allows
to use the same code for architectures that does not support non-LFS
getdents syscall).  It has two main differences to wordsize-32 one:

  - DIRENT_SET_DP_INO is added to handle alpha requirement to zero
    the padding.

  - alloca is removed by allocating a bounded temporary buffer (it
    increases stack usage by roughly 276 bytes).

The default implementation handle the Linux requirements:

  * getdents is only built for _DIRENT_MATCHES_DIRENT64 being 0.

  * getdents64 is always built and aliased to getdents for ABIs
    that define _DIRENT_MATCHES_DIRENT64 to 1.

  * A compat symbol is added for getdents64 for ABI that used to
    export the old non-LFS version.

Checked on aarch64-linux-gnu, x86_64-linux-gnu, i686-linux-gnu,
sparcv9-linux-gnu, sparc64-linux-gnu, powerpc-linux-gnu, and
powerpc64le-linux-gnu.

	* sysdeps/unix/sysv/linux/alpha/getdents.c: Add comments with alpha
	requirements.
	 (_DIRENT_MATCHES_DIRENT64): Undef
	* sysdeps/unix/sysv/linux/alpha/getdents64.c: Likewise.
	* sysdeps/unix/sysv/linux/arm/getdents64.c: Remove file.
	* sysdeps/unix/sysv/linux/generic/getdents.c: Likewise.
	* sysdeps/unix/sysv/linux/generic/getdents64.c: Likewise.
	* sysdeps/unix/sysv/linux/generic/wordsize-32/getdents.c: Likewise.
	* sysdeps/unix/sysv/linux/getdents.c: Simplify implementation by
	use getdents64 syscalls as base.
	* sysdeps/unix/sysv/linux/getdents64.c: Likewise and add compatibility
	symbol if required.
	* sysdeps/unix/sysv/linux/hppa/getdents64.c: Likewise.
	* sysdeps/unix/sysv/linux/i386/getdents64.c: Likewise.
	* sysdeps/unix/sysv/linux/m68k/getdents64.c: Likewise.
	* sysdeps/unix/sysv/linux/powerpc/getdents64.c: Likewise.
	* sysdeps/unix/sysv/linux/s390/s390-32/getdents64.c: Likewise.
	* sysdeps/unix/sysv/linux/sparc/sparc32/getdents64.c: Likewise.
	* sysdeps/unix/sysv/linux/wordsize-64/getdents.c: Likewise.
	* sysdeps/unix/sysv/linux/wordsize-64/getdents64.c: Likewise.
	* sysdeps/unix/sysv/linux/sparc/sparc64/get_clockfreq.c
	(__get_clockfreq_via_proc_openprom): Use __getdents64.
	* sysdeps/unix/sysv/linux/mips/mips64/getdents64.c: New file.