Bad permissions when install from opam with cygwin

[Et7f3]

error

 make test.opt
ocsigenserver.opt  -c local/etc/ocalc/ocalc-test.conf
ocsigenserver.opt: ocsigen:main: Fatal - While loading /home/root/.opam/ocaml-base-compiler/lib/ocsigenserver/extensions/staticmod.cmxs: error loading shared library: Permission denied
make: *** [Makefile:60: test.opt] Error 52

what I have typed to fix
chmod 755 $OPAM_SWITCH_PREFIX/lib/ocsigenserver/extensions/* maybe we can choose lesser than 755

when installing with opam in cygwin
-rw-r--r-- ************************************* staticmod.cmxs