Fix autoconf CPU detection on Raspberry Pi 3

[AlgorithMan-de]

Autoconf falsely detects an "armv7l" CPU on Cortex-A53
machines like several Raspberry Pi 3 models.

This change works around the issue by correcting the
host_cpu in configure.ac.

See also

• https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70210
• https://savannah.gnu.org/support/index.php?110360

[PeterCoghlan]

I know nothing about autoconf but I can confirm that this fix does allow me to compile Hercules on my Raspberry Pi 3 without having to disable optimisation.

When I do this, I get a warning about a possible unitinialised variable in tcpnje.c which I haven't seen before. The logic of the code ensures that the variable does get initialised but it's not obvious enough for the compiler to spot it as it happens on a previous trip around a big loop. I will look into finding a way to reassure the compiler about this.

[Fish-Git]

When I do this, I get a warning about a possible unitinialised variable in tcpnje.c which I haven't seen before. The logic of the code ensures that the variable does get initialised but it's not obvious enough for the compiler to spot it as it happens on a previous trip around a big loop. I will look into finding a way to reassure the compiler about this.

Initialize the variable at the point where it is declared.

[AlgorithMan-de]

b29ae59 also makes it work on Raspberry Pi 4. But I have communicated with the gcc and autoconf people about this and they suggested a cleaner way to integrate this fix into autoconf.ac