python3-core package provides python3.7m-config-lib script, but the python3-config symlink is provided by the python3-dev package:

packages-split$ ls -lah python3-core/usr/bin/
total 44K
drwxr-xr-x 2 user users 4.0K Oct 11 14:38 .
drwxr-xr-x 5 user users 4.0K Oct 11 14:38 ..
lrwxrwxrwx 1 user users    9 Oct 11 14:38 python3 -> python3.7
-rwxr-xr-x 4 user users  14K Oct 11 14:38 python3.7
-rwxr-xr-x 4 user users  14K Oct 11 14:38 python3.7m
-rwxr-xr-x 2 user users 1.9K Oct 11 14:38 python3.7m-config-lib

packages-split$ ls -lah python3-dev/usr/bin/
total 8.0K
drwxr-xr-x 2 user users 4.0K Oct 11 14:38 .
drwxr-xr-x 5 user users 4.0K Oct 11 14:38 ..
lrwxrwxrwx 1 user users   17 Oct 11 14:38 python3.7-config -> python3.7m-config
lrwxrwxrwx 1 user users   16 Oct 11 14:38 python3-config -> python3.7-config


Also, at the moment, python3-config seems to be missing dependencies:

$ git clone git://git.yoctoproject.org/poky
$ . poky/oe-init-build-env

local.conf:
IMAGE_INSTALL_append = " python3-core python3-dev"

$ bitbake core-image-minimal
$ runqemu qemux86-64 nographic kvm slirp

root@qemux86-64:~# python3-config
Traceback (most recent call last):
  File "/usr/bin/python3-config", line 9, in <module>
    from distutils import sysconfig
ModuleNotFoundError: No module named 'distutils'

root@qemux86-64:~# ls -lah /usr/bin/python*-config*
lrwxrwxrwx 1 root root 16 Oct 11 11:38 /usr/bin/python3-config -> python3.7-config
lrwxrwxrwx 1 root root 17 Oct 11 11:38 /usr/bin/python3.7-config -> python3.7m-config
lrwxrwxrwx 1 root root 30 Oct 11 11:45 /usr/bin/python3.7m-config -> /usr/bin/python3.7m-config-lib
-rwxr-xr-x 1 root root 1.9K Oct 11 11:38 /usr/bin/python3.7m-config-lib