It seems like currently oot-builds succeed only if the build dir and the source dir are at the same level of nesting

Steps to reproduce

; cd $osslrepo
; git checkout origin/OpenSSL_1_1_1-stable
; srcdir=$PWD
; blddir=../_build/nest/a/little/more
; mkdir -p $blddir
; cd $blddir
; $srcdir/config
; make update

Notice that if $blddir is set to ../_build, the failure is avoided.

To quote @levitte: "I have a branch!" (where I can trigger the error in Travis): https://github.com/romen/openssl/tree/issues/1.1.1/oot_build

Here you can see the build passing using ../_build as the build dir, here you can see the build failing using ../_build/nest/a/little/more instead.
Here you can see the build failing in GitHub CI: #14388.

This seems to be related to #11184 and #11185, that addressed a similar defect in master.

edit: updated to point to #14388 now that Travis CI is no more.