Note:
Without using the '--cpu' configure option the configure script will try to
guess for what architecture the code should be optimized.
The problem was noticed while trying to build an i686 target on x86-64 build
host, which utterly failed without properly specifying the target architecture.
Note:
Botan uses a custom configuration system, where the old implementation was done
in perl but the newer, recommended configure script is written python.
The python version we use since commit b8d2819e4f
of the package tree, so we need to build botan after python for having a python
interpreter available in the build.