When trying to cross-compile gentoo on arm64 for armv7  it fails for portage with the following message (note the cc1 warning):
armv7a-hardfloat-linux-gnueabi-gcc -O2 -pipe -fomit-frame-pointer -fPIC -I/usr/include/python2.7 -c src/portage_util_libc.c -o /usr/armv7a-hardfloat-linux-gnueabi/tmp/portage/sys-apps/portage-2.3.8/work/portage-2.3.8-python2_7/temp.linux-x86_64-2.7/src/portage_util_libc.o -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE
cc1: warning: include location "/usr/include/python2.7" is unsafe for cross-compilation [-Wpoison-system-directories]
In file included from /usr/include/python2.7/Python.h:58:0,
/usr/include/python2.7/pyport.h:886:2: error: #error "LONG_BIT definition appears wrong for platform (bad gcc/glibc config?)."
#error "LONG_BIT definition appears wrong for platform (bad gcc/glibc config?)."
error: command 'armv7a-hardfloat-linux-gnueabi-gcc' failed with exit status 1
Similar bug reports  exist but I decided that this might be worth an extra report since it is about portage. There is a comment  from 2017 stating:
"Cross-compiling python packages is not generally expected to work."
Is that still the case (especially for portage)?
 sudo armv7a-hardfloat-linux-gnueabi-emerge -uva --newuse @system
Set USE="-native-extensions" for sys-apps/portage.
Compiles native "C" extensions (speedups, instead of using python
backup code). Currently includes libc-locales.
This should only be temporarily disabled for some bootstrapping
operations. Cross-compilation is not supported.
Due to "Cross-compilation is not supported." I am closing this bug.