include unistd everywhere except msvc

Author: jcaselman-keysight

config/config.initialize.m

@@ -4,6 +4,10 @@
 #include "objc-common.g"
 #include <stdio.h>
 
+#if !defined(_MSC_VER)
+#include <unistd.h>
+#endif
+
 #if defined(_WIN32)
 
 #include <process.h>