message: Remove Linux-specific includes for posix/FileSystem.cpp
  Summary:
  This improves the process of cross-compiling from macOS to Linux
  since these files aren't used / needed at all.
  Reviewers: clayborg, labath
  Subscribers: lldb-commits, krytarowski
diff: #include <sys/stat.h>
  #include <sys/types.h>
  #include <unistd.h>
  -#ifdef __linux__
  -#include <linux/magic.h>
  -#include <sys/mount.h>
  -#include <sys/statfs.h>
  -#endif
  #if defined(__NetBSD__)
  #include <sys/statvfs.h>
  #endif
  