Makefile: fix flatzinc rule on windows
Makefile: fix flatzinc rule on windows

google/or-tools,google/or-tools,google/or-tools,google/or-tools,google/or-tools,or-tools/or-tools,or-tools/or-tools,google/or-tools,or-tools/or-tools,or-tools/or-tools,or-tools/or-tools,or-tools/or-tools