Fix broken pr78138.c for avr

The declaration for memcpy had the size parameter declared as 
unsigned long. For avr, __SIZE_TYPE__ is unsigned int, and 
this caused a builtin-declaration-mismatch warning, resulting
in a couple of FAILs.

Fixed by typedef'ing __SIZE_TYPE__ to size_t and using size_t as the
type for memcpy's third parameter.

From-SVN: r247483

gcc/testsuite/ChangeLog

+2017-05-02  Senthil Kumar Selvaraj  <senthil_kumar.selvaraj@atmel.com>
+
+	* gcc.dg/pr78138.c: Use __SIZE_TYPE__ instead of
+	unsigned long.
+
 2017-05-01  Xi Ruoyao  <ryxi@stu.xidian.edu.cn>
 
 	PR c++/80038

gcc/testsuite/gcc.dg/pr78138.c

@@ -5,7 +5,9 @@
 
 char d [5];
 
-void* memcpy (void*, const void*, unsigned long);
+__extension__ typedef __SIZE_TYPE__ size_t;
+
+void* memcpy (void*, const void*, size_t);
 extern char* strcpy (char*, const char*);
 
 void f (int i, int j)