Add compat wrapper for fstatat

Compat.c

@@ -0,0 +1,46 @@
+/*
+htop - Compat.c
+(C) 2020 Christian Göttsche
+Released under the GNU GPLv2, see the COPYING file
+in the source distribution for its full text.
+*/
+
+#include "config.h" // IWYU pragma: keep
+
+#include <fcntl.h>
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+
+#include "Compat.h"
+#ifndef HAVE_FSTATAT
+#include "XUtils.h"
+#endif
+
+
+int Compat_fstatat(int dirfd,
+                   const char* dirpath,
+                   const char* pathname,
+                   struct stat* statbuf,
+                   int flags) {
+
+#ifdef HAVE_FSTATAT
+
+   (void)dirpath;
+
+   return fstatat(dirfd, pathname, statbuf, flags);
+
+#else
+
+   (void)dirfd;
+
+   char path[4096];
+   xSnprintf(path, sizeof(path), "%s/%s", dirpath, pathname);
+
+   if (flags & AT_SYMLINK_NOFOLLOW)
+      return lstat(path, statbuf);
+
+   return stat(path, statbuf);
+
+#endif
+}