Require GCC 6.2 or later to build glibc

[Florian Weimer]

* Joseph Myers:

> Thus, this patch increases the minimum to 6.2, removing the
> documentation of the separate requirement for powerpc64le.  It does
> not remove the powerpc64le configure test, or any __GNUC_PREREQ that
> could be removed as not being in installed headers or files shared
> with gnulib; I think such cleanups are best done separately.

Agreed.

> 2019-01-31  Joseph Myers  <joseph@codesourcery.com>
>
> 	* configure.ac (libc_cv_compiler_ok): Require GCC 6.2 or later.
> 	* configure: Regenerated.
> 	* manual/install.texi (Tools for Compilation): Update minimum GCC
> 	version.
> 	* INSTALL: Regenerated.

Patch looks okay to me, thanks.

Florian