Define MALLOC_ABI_ALIGNMENT

The AArch64 backend currently doesn't set MALLOC_ABI_ALIGNMENT, so
add this to enable alignment optimizations on malloc pointers.
Use the same value as STACK_BOUNDARY and BIGGEST_ALIGNMENT.

    gcc/
	* config/aarch64/aarch64.h (MALLOC_ABI_ALIGNMENT): New define.

From-SVN: r254348

gcc/ChangeLog

+2017-11-02  Wilco Dijkstra  <wdijkstr@arm.com>
+
+	* config/aarch64/aarch64.h (MALLOC_ABI_ALIGNMENT): New define.
+
 2017-11-02  Jeff Law  <law@redhat.com>
 
 	* gimple-ssa-sprintf.c (sprintf_dom_walker): Remove

gcc/config/aarch64/aarch64.h

@@ -111,6 +111,9 @@
 
 #define STRUCTURE_SIZE_BOUNDARY		8
 
+/* Heap alignment (same as BIGGEST_ALIGNMENT and STACK_BOUNDARY).  */
+#define MALLOC_ABI_ALIGNMENT  128
+
 /* Defined by the ABI */
 #define WCHAR_TYPE "unsigned int"
 #define WCHAR_TYPE_SIZE			32