Add support for multiple microarchitectures in single binary

 * compiler -march= parameter is changed from native to corei7
   so code is always genereted with instructions which are available
   on the Nehalem microarchitecture (up to SSE4.2)

 * compiler -mtune= parameter is added so code is optimized for
   corei7-avx which equals to Sandy Bridge microarchitecture

 * set of macros is added which allows run-time detection of available
   cpu instructions (e.g. clib_cpu_supports_avx())

 * set of macros is added which allows us to clone graph node funcitons
   where cloned function is optmized for different microarchitecture
   Those macros are using following attributes:
     __attribute__((flatten))
     __attribute__((target("arch=core-avx2)))

   I.e. If applied to foo_node_fn() macro will generate cloned
   functions foo_node_fn_avx2() and foo_node_fn_avx512() (future)
   It will also generate function void * foo_node_fn_multiarch_select()
   which detects available instruction set and returns pointer to the
   best matching function clone.

Change-Id: I2dce0ac92a5ede95fcb56f47f3d1f3c4c040bac0
Signed-off-by: Damjan Marion <damarion@cisco.com>
diff --git a/vnet/vnet/gre/gre.c b/vnet/vnet/gre/gre.c
index 075bd6f..6d37515 100644
--- a/vnet/vnet/gre/gre.c
+++ b/vnet/vnet/gre/gre.c
@@ -454,6 +454,9 @@
 #endif
 };
 
+VLIB_DEVICE_TX_FUNCTION_MULTIARCH (gre_device_class,
+				   gre_interface_tx)
+
 
 VNET_HW_INTERFACE_CLASS (gre_hw_interface_class) = {
   .name = "GRE",