Disabled in Makefile.inc1 with a comment "PowerPC and Sparc64 need extra crt*.o files"
PowerPC has now been fixed :)
A commit references this bug:
Date: Thu Nov 7 19:37:27 UTC 2019
New revision: 354468
arch.7: claim 12.x as the last architecture with sparc64 support
GCC 4.2.1 is being removed before FreeBSD 13, as are some other
components required by FreeBSD/sparc64. Contemporary GCC does not build
and there is currently no indication that anyone is going to address
PR: 228919, 233405, 236839, 239851
Attempting to build for sparc64 with external toolchain in a GPL-removed FreeBSD tree fails in "stage 4.2: building libraries" with:
/usr/local/bin/sparc64-unknown-freebsd12.0-ld: cannot find crtendS.o: No such file or directory
collect2: error: ld returned 1 exit status
For reference, PPC was fixed in r342974.
See also https://reviews.freebsd.org/D23122