Require Linux 3.2 except on x86 / x86_64, 3.2 headers everywhere.

Require Linux 3.2 except on x86 / x86_64, 3.2 headers everywhere.

In <https://sourceware.org/ml/libc-alpha/2016-01/msg00885.html> I
proposed a minimum Linux kernel version of 3.2 for glibc 2.24, since
Linux 2.6.32 has reached EOL.

In the discussion in February, some concerns were expressed about
compatibility with OpenVZ containers.  It's not clear that these are
real issues, given OpenVZ backporting kernel features and faking the
kernel version for guest software, as discussed in
<https://sourceware.org/ml/libc-alpha/2016-02/msg00278.html>.  It's
also not clear that supporting running GNU/Linux distributions from
late 2016 (at the earliest) on a kernel series from 2009 is a sensible
expectation.  However, as an interim step, this patch increases the
requirement everywhere except x86 / x86_64 (since the controversy was
only about those architectures); the special caveats and settings can
easily be removed later when we're ready to increase the requirements
on x86 / x86_64 (and if someone would like to raise the issue on LWN
as suggested in the previous discussion, that would be welcome).  3.2
kernel headers are required everywhere by this patch.

(x32 already requires 3.4 or later, so is unaffected by this patch.)

As usual for such a change, this patch only changes the configure
scripts and associated documentation.  The intent is to follow up with
removal of dead __LINUX_KERNEL_VERSION conditionals.  Each __ASSUME_*
or other macro that becomes dead can then be removed independently.

Tested for x86_64 and x86.

	* sysdeps/unix/sysv/linux/configure.ac (LIBC_LINUX_VERSION):
	Define to 3.2.0.
	(arch_minimum_kernel): Likewise.
	* sysdeps/unix/sysv/linux/configure: Regenerated.
	* sysdeps/unix/sysv/linux/i386/configure.ac (arch_minimum_kernel):
	Define to 2.6.32.
	* sysdeps/unix/sysv/linux/i386/configure: Regenerated.
	* sysdeps/unix/sysv/linux/x86_64/64/configure.ac
	(arch_minimum_kernel): Define to 2.6.32.
	* sysdeps/unix/sysv/linux/x86_64/64/configure: Regenerated.
	* README: Document Linux 3.2 requirement.
	* manual/install.texi (Linux): Document Linux 3.2 headers
	requirement.
	* INSTALL: Regenerated.