I just noticed I have a successful build from pkgsrc last year:
ls -l /usr/pkg/bin/ksh93 && file /usr/pkg/bin/ksh93 18-09-02 - 11:33:37
-rwxr-xr-x 1 root wheel 1501856 Jun 17 2017 /usr/pkg/bin/ksh93
/usr/pkg/bin/ksh93: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /usr/libexec/ld.elf_so, for NetBSD 8.99.1, stripped
Anyway, I *think* it would be better to get the git version. I notice the required build tools are already in, albeit a bit behind (py-meson and ninja-build).
* ( 'think' being just an operative term ).