glsl: remove extern "C" around #includes

Reviewed-by: Anuj Phogat <anuj.phogat@gmail.com>
Reviewed-by: Jose Fonseca <jfonseca@vmware.com>
diff --git a/src/glsl/linker.cpp b/src/glsl/linker.cpp
index 6713df1..44468c7 100644
--- a/src/glsl/linker.cpp
+++ b/src/glsl/linker.cpp
@@ -76,10 +76,9 @@
 #include "ir_rvalue_visitor.h"
 #include "ir_uniform.h"
 
-extern "C" {
 #include "main/shaderobj.h"
 #include "main/enums.h"
-}
+
 
 void linker_error(gl_shader_program *, const char *, ...);