glsl: resolve extern C workarounds/hacks

Do not wrap header inclusion in extern C since it can cause issues.

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>
Reviewed-by: Brian Paul <brianp@vmware.com>

src/compiler/glsl/glsl_symbol_table.h

@@ -28,9 +28,7 @@
 
 #include <new>
 
-extern "C" {
 #include "program/symbol_table.h"
-}
 #include "ir.h"
 
 class symbol_table_entry;