Raise an error when calling make with MARCHes known to fail

[nalimilan]

Pre-SSE2 CPUs are not supported as some tests fail (#7185).
Better warn as soon as possible.

[yuyichao]

The only issue I can see is that some distro maintainers might want to support older architectures (and for cases it works reasonably well...).

[nalimilan]

Yeah, this was discussed on the other issue. For Fedora, I'm supposed to make i386 or i686-compatible builds. But in practice, better a Pentium4 build than nothing, and I don't think anybody would notice.

Shipping a build which doesn't pass the tests sounds like a very bad idea to me, especially if that's just to pretend supporting machines that nobody uses.

[yuyichao]

Good enough for me. (I've also changed my ArchLinux julia-git package to pentium4 and claiming i686 arch)...

Just want to raise a concern I've seen from distro maintainers but if it has already been discussed I'll be totally find with it.

[tkelman]

Actually we build 32-bit binaries right now with

MARCH = i686
JULIA_CPU_TARGET = pentium4

since there was a bug having to do with 32 bit calling convention in one of the dependencies, I think SuiteSparse.

[nalimilan]

@tkelman Interesting. So JULIA_CPU_TARGET is what matters for this issue? I guess I should check for that variable instead, and suggest passing MARCH=i686 JULIA_CPU_TARGET=pentium4 OR MARCH=pentium4 if you don't build the dependencies. FWIW, the latter works fine in Fedora, and it would be a shame not to use SSE2 everywhere in Julia if we require it.

[tkelman]

I agree but if we're going to adjust the buildbot configuration we should carefully test all 32-bit platforms on both release-0.3 and master first, to make sure it doesn't bring back any bugs.

[nalimilan]

@tkelman Sorry, I had missed your comment. I wasn't really suggesting to change the buildbots right now -- just to give both suggestions to the user.

OK to merge the updated version?

[tkelman]

I don't think I've built successfully with MARCH=i386, I typically use i686.

[nalimilan]

OK, changed to i686.

[tkelman]

I pushed a commit here to make sure this doesn't break 32 bit appveyor

[tkelman]

my mistake, sorry, I already covered this in

julia/contrib/windows/msys_build.sh

Line 49 in f3a6461

echo "override JULIA_CPU_TARGET = pentium4" >> Make.user