Require GCC 5 or later to build glibc (bug 23993).

We know that building glibc with GCC 4.9 is broken on various
platforms (bug 23993).  As it's more than a year since we last
increased the minimum GCC version to build glibc, this patch changes
the requirement to be GCC 5 or later (indeed, based on 4.9 having been
required for building 2.26, it would be consistent in terms of timing
to require GCC 6 or later from the 2.30 release onwards).  It
deliberately just updates the configure test and corresponding
documentation, leaving removal of no-longer-needed __GNUC_PREREQ tests
for a separate patch.

In the NEWS entry, the requirement for a newer GCC version for
powerpc64le is reiterated (as in the entry for the 4.9 requirement in
2.26) to avoid suggesting the version requirement there has gone down.
(If that version goes up further as part of support for binary128 long
double, of course the wording would change at that time.)

Tested for x86_64.

	[BZ #23993]
	* configure.ac (libc_cv_compiler_ok): Require GCC 5 or later.
	* configure: Regenerated.
	* manual/install.texi (Tools for Compilation): Update minimum GCC
	version.
	* INSTALL: Regenerated.

1 files changed, 6 insertions, 0 deletions

diff --git a/NEWS b/NEWS
index 300e978..cd29ec7 100644
--- a/NEWS
+++ b/NEWS
@@ -72,6 +72,12 @@ Changes to build and runtime requirements:
 
 * Python 3.4 or later is required to build the GNU C Library.
 
+* On most architectures, GCC 5 or later is required to build the GNU C
+  Library.  (On powerpc64le, GCC 6.2 or later is still required, as before.)
+
+  Older GCC versions and non-GNU compilers are still supported when
+  compiling programs that use the GNU C Library.
+
 Security related changes:
 
   CVE-2018-19591: A file descriptor leak in if_nametoindex can lead to a