need help to investigate an ocaml build error on ppc64le archi

Hello there,
I am trying to investigate a failure while porting ocaml on ppc64le archi (flag1)
This is most probably related to some changes I did not made yet.
But because I do not understand anything about ocaml I do not know where to search.

I understand that the bad unix.o is generated by the call to ocamlcompopt.sh
calling itself ocamlrun with the parameters of (flag2).

But I do not understand what archi specific files are used by this command line.

I would appreciate any suggestion on the subject.

flag1: the original failure log extract.
===
make[2]: Entering directory `/home/michel/rpmbuild/BUILD/ocaml-4.01.0/otherlibs/unix'
../../ocamlcompopt.sh -c -w +33..39 -warn-error A -g -nolabels unix.ml
../../ocamlcompopt.sh -c -w +33..39 -warn-error A -g -nolabels unixLabels.ml
../../boot/ocamlrun ../../tools/ocamlmklib -o unix -oc unix -ocamlopt '../../ocamlcompopt.sh' -linkall \
          unix.cmx unixLabels.cmx
../../ocamlcompopt.sh -shared -o unix.cmxs -I . unix.cmxa
/usr/bin/ld: unix.cmxs.startup.o: ABI version 1 is not compatible with ABI version 2 output
/usr/bin/ld: failed to merge target specific data of file unix.cmxs.startup.o
/usr/bin/ld: unix.a(unix.o): ABI version 1 is not compatible with ABI version 2 output
/usr/bin/ld: failed to merge target specific data of file unix.a(unix.o)
/usr/bin/ld: unix.a(unixLabels.o): ABI version 1 is not compatible with ABI version 2 output
/usr/bin/ld: failed to merge target specific data of file unix.a(unixLabels.o)
collect2: error: ld returned 1 exit status
===

flag2: unix.o generated from unix.ml
===
+ exec ../../boot/ocamlrun ../../ocamlopt -nostdlib -I ../../stdlib -c -w +33..39 -warn-error A -g -nolabels unix.ml
===
$file unix.ml
unix.ml: Mathematica 3.0 notebook
===
$readelf -h unix.o |grep Flags
   Flags:                             0x0
===

-- 
Michel Normand