devel/llvm13 failed to reclaim memory on 8 GB Pi4 running -current

Attempts to compile devel/llvm13 on a Pi4 running -current (updated
on 20220126) with 8 GB of RAM and 8 GB of swap has failed on two occasions using 
make -DBATCH > make.log & 
in /usr/ports/devel/llvm13 using the system compiler. The system is
self-hosted. 

The first failure reported clang error 139, but the second
was different, reporting only:
FAILED: tools/flang/lib/Evaluate/CMakeFiles/obj.FortranEvaluate.dir/check-expression.cpp.o
along with a console report of
+swap_pager: indefinite wait buffer: bufobj: 0, blkno: 1258432, size: 4096
+swap_pager: indefinite wait buffer: bufobj: 0, blkno: 627221, size: 8192
+swap_pager: indefinite wait buffer: bufobj: 0, blkno: 240419, size: 4096
+swap_pager: out of swap space
+swp_pager_getswapspace(12): failed
+pid 61012 (c++), jid 0, uid 0, was killed: failed to reclaim memory

Swap use peaked a little over 50%. After the first failure a restart
of make using MAKE_JOBS_UNSAFE=yes ran to completion with one thread.

A copy of the build log, logging script and other notes is at
http://www.zefox.net/~fbsd/rpi4/20220127/

Clang error 139 has been seen several times during make buildworld on a Pi3 running
stable/13 with 2 GB of swap as well. Perhaps the two failures are related. The Pi3 
failures didn't report out of swap, all were clang error 139 with "failed to reclaim 
memory". Even with only 1 thread (j1) the failure reproduced.

Thanks for reading,

bob prohaska
20220127