r352239: install failure: make[10]: exec(btxld) failed (No such file or directory)

Hello,

we install several pkg-based systems and poudriere from a dedicated tree of
sources, instead of /usr/src it is in our case /pool/sources/CURRENT/src and
12-STABLE/src. Compilation of the sources is done within a JAIL!

For a couple of days now, both trees, CURRENT (r352239 now) and 12-STABLE
(r352239) fail at the exact same point, when compiling and further packaging:

[...]
install -U -M
/pool/sources/CURRENT/obj/pool/sources/CURRENT/src/amd64.amd64/worldstage//METALOG
-D /pool/sources/CURRENT/obj/pool/sources/CURRENT/src/amd64.amd64/worldstage -T
package=utilities -d -m 0755 -o root  -g wheel
/pool/sources/CURRENT/obj/pool/sources/CURRENT/src/amd64.amd64/worldstage/boot
objcopy -S -O binary boot2.out boot2.bin btxld -v -E 0x2000 -f bin -b
/pool/sources/CURRENT/obj/pool/sources/CURRENT/src/amd64.amd64/stand/i386/btx/btx/btx
-l boot2.ldr  -o boot2.ld -P 1 boot2.bin make[10]: exec(btxld) failed (No such
file or directory) *** Error code 1
[...]

For reduction of the installed binaries and stuff, we use customized src.conf
and each build process is delegated to its appropriate src.conf by setting the
variabel SRCCONF accordingly; poudriere also uses the same src.conf by linking
the jailname-src.conf file into poudriere's config folder; the content of
src.conf is as follows:

[...]
WITH_OFED=                              YES
#WITH_CTF=                              YES
#
#WITH_BEARSSL=                          YES
#
WITH_SVN=                               YES
#
WITH_SORT_THREADS=                      YES
#
MALLOC_PRODUCTION=                      YES
#
#WITHOUT_ASSERT_DEBUG=                  YES
#WITHOUT_DEBUG_FILES=        YES
#WITHOUT_TESTS=              YES
WITHOUT_PROFILE=            YES
#
WITHOUT_REPRODUCIBLE_BUILD=     YES
#
#  mitigation for CVE-2017-5715 in the kernel build
WITH_RETPOLINE=                         YES

[...]

Building poudriere jails from such sources also fails since a couple of days on
all platforms with a weird message thata folder and/or file atf-check is
missing (this happens when using command sequence: poudriere jail -j jailname
-u -b and the install method of the appropriate jail is src=/path/to/source/src.

Thanks for helping,

oh