ACPI: eliminate spurious unused variables warning w.r.t. ACPI_MODULE_NAME

drivers/acpi/include/acmacros.h

 /******************************************************************************
  *
  * Name: acmacros.h - C macros for the entire subsystem.
- *       $Revision: 132 $
+ *       $Revision: 133 $
  *
  *****************************************************************************/
 
@@ -398,7 +398,7 @@
 
 #ifdef ACPI_DEBUG_OUTPUT
 
-#define ACPI_MODULE_NAME(name)               static char *_THIS_MODULE = name;
+#define ACPI_MODULE_NAME(name)               static char ACPI_UNUSED_VAR *_THIS_MODULE = name;
 
 /*
  * Function entry tracing.

drivers/acpi/include/platform/acgcc.h

 /******************************************************************************
  *
  * Name: acgcc.h - GCC specific defines, etc.
- *       $Revision: 23 $
+ *       $Revision: 24 $
  *
  *****************************************************************************/
 
@@ -31,4 +31,11 @@
  */
 #define ACPI_PRINTF_LIKE_FUNC __attribute__ ((__format__ (__printf__, 4, 5)))
 
+/* Some compilers complain about unused variables. Sometimes we don't want to
+ * use all the variables (most specifically for _THIS_MODULE). This allow us
+ * to to tell the compiler warning in a per-variable manner that a variable
+ * is unused.
+ */
+#define ACPI_UNUSED_VAR __attribute__ ((unused))
+
 #endif /* __ACGCC_H__ */