Z3 4.8.5 build on Cygwin fails on flexlink -fopenmp

[btj]

Build https://travis-ci.org/verifast/vfdeps-win/builds/562820769 fails here:

ocamlmklib -o api/ml/z3ml -I api/ml api/ml/z3native_stubs.o api/ml/z3enums.cmo api/ml/z3native.cmo api/ml/z3.cmo  -cclib -lz3 -cclib -fopenmp -cclib -static-libgcc -cclib -static-libstdc++
ocamlfind ocamlopt -package num  -I api/ml -o api/ml/z3enums.cmx -c ../src/api/ml/z3enums.ml
ocamlfind ocamlopt -package num  -I api/ml -o api/ml/z3native.cmx -c ../src/api/ml/z3native.ml
ocamlfind ocamlopt -package num  -I api/ml -o api/ml/z3.cmx -c ../src/api/ml/z3.ml
ocamlmklib -o api/ml/z3ml -I api/ml api/ml/z3native_stubs.o  api/ml/z3enums.cmx api/ml/z3native.cmx api/ml/z3.cmx -cclib -lz3 -cclib -fopenmp -cclib -static-libgcc -cclib -static-libstdc++
ocamlfind ocamlopt -package num  -linkall -shared -o api/ml/z3ml.cmxs -I . -I api/ml api/ml/z3ml.cmxa
make[1]: Leaving directory '/cygdrive/c/Users/travis/build/verifast/vfdeps-win/z3-Z3-4.8.5/build'
flexlink: unknown option '-fopenmp'.
File "caml_startup", line 1:
Error: Error during linking
make[1]: *** [Makefile:4464: api/ml/z3ml.cmxs] Error 2

I'm guessing that the -cclib -fopenmp arguments to ocamlmklib should be -cclib -link -cclib -fopenmp to ensure the -fopenmp is passed to the actual linker. Of course, the question is whether the -fopenmp flag is compatible with Cygwin at all.

[btj]

Z3's build/Makefile file is generated by scripts/mk_util.py. Search for ocamlmklib. It's in the mk_makefile method of class MLComponent:

            OCAMLMKLIB = 'ocamlmklib'

            LIBZ3 = '-cclib -l' + z3link
            if is_cygwin() and not(is_cygwin_mingw()):
                LIBZ3 = z3linkdep

            LIBZ3 = LIBZ3 + ' ' + ' '.join(map(lambda x: '-cclib ' + x, LDFLAGS.split()))

            if DEBUG_MODE and not(is_cygwin()):
                # Some ocamlmklib's don't like -g; observed on cygwin, but may be others as well.
                OCAMLMKLIB += ' -g'

            z3mls = os.path.join(self.sub_dir, 'z3ml')

            out.write('%s.cma: %s %s %s\n' % (z3mls, cmos, stubso, z3linkdep))
            out.write('\t%s -o %s -I %s %s %s %s\n' % (OCAMLMKLIB, z3mls, self.sub_dir, stubso, cmos, LIBZ3))
            out.write('%s.cmxa: %s %s %s %s.cma\n' % (z3mls, cmxs, stubso, z3linkdep, z3mls))
            out.write('\t%s -o %s -I %s %s %s %s\n' % (OCAMLMKLIB, z3mls, self.sub_dir, stubso, cmxs, LIBZ3))
            out.write('%s.cmxs: %s.cmxa\n' % (z3mls, z3mls))
            out.write('\t%s -linkall -shared -o %s.cmxs -I . -I %s %s.cmxa\n' % (OCAMLOPTF, z3mls, self.sub_dir, z3mls))

            out.write('\n')
            out.write('ml: %s.cma %s.cmxa %s.cmxs\n' % (z3mls, z3mls, z3mls))
            out.write('\n')

Interestingly, when I try the build locally, it fails with a different error:

flexlink: unknown option -static-libgcc

In this build, the -fopenmp flag is not included in the command line:

api/ml/z3ml.cma: api/ml/z3enums.cmo api/ml/z3native.cmo api/ml/z3.cmo  api/ml/z3native_stubs$(OBJ_EXT) libz3$(SO_EXT)
        ocamlmklib -o api/ml/z3ml -I api/ml api/ml/z3native_stubs$(OBJ_EXT) api/ml/z3enums.cmo api/ml/z3native.cmo api/ml/z3.cmo  -cclib -lz3 -cclib -static-libgcc -cclib -static-libstdc++
api/ml/z3ml.cmxa:  api/ml/z3enums.cmx api/ml/z3native.cmx api/ml/z3.cmx api/ml/z3native_stubs$(OBJ_EXT) libz3$(SO_EXT) api/ml/z3ml.cma
        ocamlmklib -o api/ml/z3ml -I api/ml api/ml/z3native_stubs$(OBJ_EXT)  api/ml/z3enums.cmx api/ml/z3native.cmx api/ml/z3.cmx -cclib -lz3 -cclib -static-libgcc -cclib -static-libstdc++
api/ml/z3ml.cmxs: api/ml/z3ml.cmxa
        ocamlfind ocamlopt -package num  -linkall -shared -o api/ml/z3ml.cmxs -I . -I api/ml api/ml/z3ml.cmxa

[btj]

I confirmed that replacing -cclib -static-libgcc by -cclib -link -cclib -static-libgcc causes the subsequent ocamlopt call (which calls flexlink) to succeed.