Require binutils 2.20 or later to build glibc

[David Miller]

From: "Joseph S. Myers" <joseph@codesourcery.com>
Date: Fri, 24 Feb 2012 22:24:43 +0000 (UTC)

> I tested building glibc on x86_64 with different binutils versions.  2.22, 
> 2.21.1a and 2.20.1a worked (I didn't test if the resulting glibc worked, 
> but it built).  2.19.1a first failed with the configure logic problem 
> described in <http://sourceware.org/ml/libc-alpha/2012-02/msg00603.html> 
> meaning multi-arch was enabled though unsupported; with that patch or 
> --disable-multi-arch, the build still failed, because 
> gnu_indirect_function is used unconditionally for x86_64, e.g. in 
> sysdeps/unix/sysv/linux/x86_64/time.c, not just for multi-arch (the case 
> there is an IFUNC depending on kernel vDSO availability).
> 
> So releases before 2.20 won't work for x86_64, which means building with 
> older versions is likely not to be particularly well tested even if there 
> are other architectures for which a build succeeds.  So I propose 2.20 as 
> a minimum version requirement for binutils for configure to enforce and 
> the installation instructions to document.
> 
> binutils 2.20 was released in October 2009.

This looks great, I'll be able to remove a lot of configure checks
and CPP conditionalized assembler on Sparc thanks to this.