config: Add explicit support for building on ESX.

The ESX userspace looks quite a bit like linux, but has some key
differences which need to be specially handled in the build.  To
distinguish between ESX and systems which use the linux datapath
module, this patch adds two new macros "ESX" and "LINUX_DATAPATH".
It uses these macros to disable building code on ESX which only
applies to a true Linux environment.  In addition, it adds a new
route-table-stub implementation which is required for the build to
complete successfully on ESX.

Signed-off-by: Ethan Jackson <ethan@nicira.com>

lib/command-line.c

@@ -92,7 +92,7 @@ run_command(int argc, char *argv[], const struct command commands[])
 
 /* Process title. */
 
-#ifdef __linux__
+#ifdef LINUX_DATAPATH
 static char *argv_start;       /* Start of command-line arguments in memory. */
 static size_t argv_size;       /* Number of bytes of command-line arguments. */
 static char *saved_proctitle;  /* Saved command-line arguments. */
@@ -179,7 +179,7 @@ proctitle_restore(void)
         saved_proctitle = NULL;
     }
 }
-#else  /* !__linux__ */
+#else  /* !LINUX_DATAPATH*/
 /* Stubs that don't do anything on non-Linux systems. */
 
 void
@@ -196,4 +196,4 @@ void
 proctitle_restore(void)
 {
 }
-#endif  /* !__linux__ */
+#endif  /* !LINUX_DATAPATH */