Fix OpenMPI Error in Cygwin
===

When I try to compiler John The Ripper with the MPI option in Cygwin, it gives the following error:

    mpicc -DHAVE_MPI -c -Wall -O2 -fomit-frame-pointer -I/usr/local/include     -mpreferred-stack-boundary=4 -msse2 -m32 -funroll-loops john-mpi.c
    Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 16.00.30319.01 for 80x86
    Copyright (C) Microsoft Corporation.  All rights reserved.
    
    cl : Command line warning D9002 : ignoring unknown option '-fomit-frame-pointer'
    cl : Command line warning D9002 : ignoring unknown option '-mpreferred-stack-boundary=4'
    cl : Command line warning D9002 : ignoring unknown option '-msse2'
    cl : Command line warning D9002 : ignoring unknown option '-m32'
    cl : Command line warning D9002 : ignoring unknown option '-funroll-loops'
    john-mpi.c
    C:\cygwin\bin/../include\mpi.h(260) : warning C4668: 'OPAL_BUILD_PLATFORM_COMPILER_VERSION' is not defined as a preprocessor macro, replacing with '0' for '#if/#elif'
    C:\cygwin\bin/../include\mpi.h(999) : warning C4668: 'HAVE_FLOAT__COMPLEX' is not defined as a preprocessor macro, replacing with '0' for '#if/#elif'
    C:\cygwin\bin/../include\mpi.h(1003) : warning C4668: 'HAVE_DOUBLE__COMPLEX' is not defined as a preprocessor macro, replacing with '0' for '#if/#elif'
    C:\cygwin\bin/../include\mpi.h(1006) : warning C4668: 'HAVE_LONG_DOUBLE__COMPLEX' is not defined as a preprocessor macro, replacing with '0' for '#if/#elif'
    c:\jtr\src\john-mpi.h(10) : warning C4255: 'id2string' : no function prototype given: converting '()' to '(void)'
    john-mpi.c(5) : fatal error C1083: Cannot open include file: 'unistd.h': No such file or directory
    Makefile:1658: recipe for target `john-mpi.o' failed
    make[1]: *** [john-mpi.o] Error 2
    make[1]: Leaving directory `/cygdrive/c/jtr/src'
    Makefile:1206: recipe for target `win32-cygwin-x86-sse2' failed
    make: *** [win32-cygwin-x86-sse2] Error 2

To use `cl.exe`, I use the following batch script:

    call "%VS100COMNTOOLS%vsvars32.bat"
    start /MAX C:\cygwin\bin\mintty.exe - rem this starts cygwin shell

Can anyone tell me how to fix this?