12-STABLE: poudriere jail installation/updating is failing

Recently an error seem to have spread across our 12-STABLE platforms offering
poudriere. Building the binaries for FreeBSD 12-STABLE (recent version r347613)
on systems running FreeBSD 12-STABLE (r347613) worked very well before, but now
the install process seem to fail on all boxes the very same way; see the error
below.

Building the binary system runs smooth. The sources are outside /usr/src and
setting

"env MAKEOBJDIRPREIX=/path/to/source/obj"

in /usr/local/etc/poudriere.d/jailname-poudriere.conf reflects that. This
source tree is built with the very same src.conf and make.conf files as
poudriere would then use for the installation via option

poudriere jail -c jail-name -m=/path/to/source/src ... (ZFS is the target
filesystem)

Any idea what causes this behaviour? On recent CURRENT, building the 12-STABLE
jail with the very same revision of 12-STABLE and the very same poudriere
config files (those residing in /usr/local/etc/poudriere.d/) works like a
charme.

Thanks in advance,

oh

[...]

install -N /pool/sources/12-STABLE/src/etc  -o root -g wheel -m 444
getopt_long.3.gz  /pool/poudriere/jails/12amd64/usr/share/man/man3/
--- realinstall_subdir_libexec ---
A failure has been detected in another branch of the parallel make

make[5]: stopped in /pool/sources/12-STABLE/src/libexec/hyperv
--- realinstall_subdir_lib ---
install -N /pool/sources/12-STABLE/src/etc  -o root -g wheel -m 444
getsubopt.3.gz  /pool/poudriere/jails/12amd64/usr/share/man/man3/
--- realinstall_subdir_libexec ---
*** [realinstall_subdir_libexec/hyperv] Error code 2

make[4]: stopped in /pool/sources/12-STABLE/src/libexec
1 error

make[4]: stopped in /pool/sources/12-STABLE/src/libexec
*** [realinstall_subdir_libexec] Error code 2

make[3]: stopped in /pool/sources/12-STABLE/src
--- realinstall_subdir_lib ---
install -N /pool/sources/12-STABLE/src/etc  -o root -g wheel -m 444
hcreate.3.gz  /pool/poudriere/jails/12amd64/usr/share/man/man3/