ir_to_mesa: Move some things outside the 'extern "C"' blocks

Having a few of these includes or forward declarations inside the
'extern "C"' block can cause problems later.  Specifically, it
prevents C++ linkage functions from being added to ir_to_mesa.h and
makes G++ angry if 'struct foo' is seen both inside and outside an
'extern "C"'.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/glsl/ir_set_program_inouts.cpp

@@ -34,10 +34,8 @@
  * from the GLSL IR.
  */
 
-extern "C" {
 #include "main/core.h" /* for struct gl_program */
 #include "program/hash_table.h"
-}
 #include "ir.h"
 #include "ir_visitor.h"
 #include "glsl_types.h"