mybuild: conflicts with bytecode only compilers

[mseri]

Fails with:

#=== ERROR while compiling mybuild.6 ==========================================#
# context              2.2.0~alpha4~dev | linux/arm32 | ocaml-base-compiler.5.1.0 | file:///home/opam/opam-repository
# path                 ~/.opam/5.1/.opam-switch/build/mybuild.6
# command              ~/.opam/opam-init/hooks/sandbox.sh build make
# exit-code            2
# env-file             ~/.opam/log/mybuild-7-9481c4.env
# output-file          ~/.opam/log/mybuild-7-9481c4.out
### output ###
# fatal: not a git repository: '.git'
# ocamlbuild -use-ocamlfind -no-links -j 0  mybuild.cma mybuild.cmxa mybuild_write_version.native
# ocamlfind ocamldep -package ocamlbuild -modules mybuild.mli > mybuild.mli.depends
# ocamlfind ocamlc -c -package ocamlbuild -o mybuild.cmi mybuild.mli
# ocamlfind ocamldep -package ocamlbuild -modules mybuild.ml > mybuild.ml.depends
# ocamlfind ocamlc -c -package ocamlbuild -o mybuild.cmo mybuild.ml
# ocamlfind ocamlc -a -package ocamlbuild mybuild.cmo -o mybuild.cma
# ocamlfind ocamlopt -c -package ocamlbuild -o mybuild.cmx mybuild.ml
# + ocamlfind ocamlopt -c -package ocamlbuild -o mybuild.cmx mybuild.ml
# ocamlfind: Not supported in your configuration: ocamlopt
# Command exited with code 2.
# make: *** [Makefile:15: build] Error 10

[mseri]

Seen on #24884