mesa: only include ctype.h where it's used

Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Jose Fonseca <jfonseca@vmware.com>
diff --git a/src/glsl/linker.cpp b/src/glsl/linker.cpp
index 3f5eac1..e11b6fa 100644
--- a/src/glsl/linker.cpp
+++ b/src/glsl/linker.cpp
@@ -64,6 +64,7 @@
  * \author Ian Romanick <ian.d.romanick@intel.com>
  */
 
+#include <ctype.h>
 #include "main/core.h"
 #include "glsl_symbol_table.h"
 #include "glsl_parser_extras.h"