Hi Guix!

The attached patch lets (guix cpu) recognize other architectures. The
code of (current-cpu) is based on the content of /proc/cpuinfo which
can be pretty different on non-intel architectures. For instance,
here's a sample from an armhf machine:

processor	: 0
model name	: ARMv7 Processor rev 4 (v7l)
BogoMIPS	: 45.47
Features	: half thumb fastmult vfp edsp thumbee neon vfpv3 tls
vfpv4 idiva idivt vfpd32 lpae evtstrm CPU implementer	: 0x41
CPU architecture: 7
CPU variant	: 0x0
CPU part	: 0xc07
CPU revision	: 4

In particular, there's no flags entry, so (current-cpu) doesn't stop
until eof, and returns #f.

It's an issue because a test uses this code, for testing manifests with
--tune. If no cpu is returned, the test crashes:

In guix/transformations.scm:
   864:25  1 (_ _ _ _ ((package ad-hoc-package "gcc-toolchain")
(<E2><80><A6>) <E2><80><A6>)) In guix/cpu.scm:
     94:2  0 (cpu->gcc-architecture #f)

Since the test fails, the "guix" package doesn't build, and I can't
reconfigure on armhf or aarch64. (well armhf has other issues right
now...)

The attached patch changes the logic of the code to read all lines,
find information about the CPU even if it's an ARM CPU, and returns
always something (to prevent the crash) when it reads eof. This means
that it will return architecture information about the last CPU,
instead of the first. I don't think that's an issue because this code
is used for --tune which really only works on intel where you don't
have multiple CPUs with too different features.

WDYT?