mesa: Fix C++ includes in sampler.cpp

Some C++ header files were included in an extern "C" block. When building with
Clang, this caused the build to fail due to namespace errors. (GCC did not
report any errors.)

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Brian Paul <brianp@vmware.com>

src/mesa/program/sampler.cpp

@@ -23,15 +23,15 @@
  * DEALINGS IN THE SOFTWARE.
  */
 
-#include <stdio.h>
+#include <cstdio>
+#include "ir.h"
+#include "glsl_types.h"
+#include "ir_visitor.h"
 
 extern "C" {
 #include "main/compiler.h"
 #include "main/mtypes.h"
 #include "program/prog_parameter.h"
-#include "ir.h"
-#include "ir_visitor.h"
-#include "glsl_types.h"
 }
 
 static void fail_link(struct gl_shader_program *prog, const char *fmt, ...) PRINTFLIKE(2, 3);