POWER build failure due to scv instruction

[Florian Weimer]

Building libc-start.o fails on powerpc64le-linux-gnu with:

…/csu/libc-start.s:623: Error: unrecognized opcode: `scv'

And indeed this can be reproduced with:

        .machine power8
        .text
        scv 0

This seems to happen with only some binutils versions.  Specifically, I
see it with 4100e6999664833defb8ee038f75812d9b85f9c7 from
binutils-2_35-branch, but oddly enough not with Fedora's 2.35.1-21.fc34
version, which is why I haven't reported this so far.

In any case, NEWS and INSTALL need to be updated with the appropriate
binutils version requirement.  If scv instruction support is required,
that would be 2.29, I think, but better double-check this.

Thanks,
Florian
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