stdlib: conditionalise unistd.h

unistd.h is the standard Unix header.  The standard library may be built
for Windows, which is not a Unix.  Guard the inclusion.

Author: compnerd

stdlib/public/stubs/LibcShims.cpp

@@ -23,7 +23,9 @@
 
 #include <stdio.h>
 #include <sys/types.h>
+#if defined(__unix__) || (defined(__APPLE__) && defined(__MACH__))
 #include <unistd.h>
+#endif
 
 #include <type_traits>