bug#44422: AC_CANONICAL_HOST sets wrong $host_cpu on Raspberry Pi 3

[Viktor Engelmann]

I'm trying to port a project to docker and I'm also testing it on my
Raspberry Pi 3B+

when I *./configure* and *make* the project, it fails with this message

gcc: error: unrecognized -mcpu target: armv7l
gcc: note: valid arguments are: arm8 arm810 strongarm [...] cortex-a53 [...]
gcc: error: missing argument to '-march='

lscpu says this:

Architecture:        armv7l
Byte Order:          Little Endian
CPU(s):              4
On-line CPU(s) list: 0-3
Thread(s) per core:  1
Core(s) per socket:  4
Socket(s):           1
Vendor ID:           ARM
Model:               4
Model name:          Cortex-A53
Stepping:            r0p4
CPU max MHz:         1200.0000
CPU min MHz:         600.0000
BogoMIPS:            38.40
Flags:               half thumb fastmult vfp edsp neon vfpv3 tls vfpv4
idiva idi
                     vt vfpd32 lpae evtstrm crc32

So it seems to me that AC_CANONICAL_HOST sets $host_cpu to armv7l,
although that is the Architecture and should be passed to -march
instead. -mcpu should get the Model name.

I couldn't get it to accept the --host=cpu-os-abi parameter, because
cortex-a35 contains a dash and that seems to confuse autoconf (that
produces the error message Invalid configuration
`cortex-a53-unknown-linux-gnueabihf': machine `cortex-a53-unknown' not
recognized). I did manage to compile with
--host=native-unknown-linux-gnueabihf, but I'd rather not define a fixed
ABI, because that would break the cross-platform compatibility of the
Dockerfile.

I'm using autoconf 2.69 from the docker base image "ubuntu:latest".