Don't skip gdb.asm/asm-source.exp on aarch64

This patch adds gdb.asm/aarch64.inc, so asm-source.exp isn't skipped
on aarch64 any more.

gdb/testsuite:

2015-09-16  Yao Qi  <yao.qi@linaro.org>

	* gdb.asm/asm-source.exp: Set asm-arch for
	aarch64*-*-* target.
	* gdb.asm/aarch64.inc: New file.

gdb/testsuite/ChangeLog

@@ -1,3 +1,9 @@
+2015-09-16  Yao Qi  <yao.qi@linaro.org>
+
+	* gdb.asm/asm-source.exp: Set asm-arch for
+	aarch64*-*-* target.
+	* gdb.asm/aarch64.inc: New file.
+
 2015-09-15  Pierre-Marie de Rodat  <derodat@adacore.com>
 
 	* gdb.ada/array_of_variable_length.exp: New testcase.

gdb/testsuite/gdb.asm/aarch64.inc

@@ -0,0 +1,34 @@
+	comment "subroutine prologue"
+	.macro gdbasm_enter
+	stp x29, x30, [sp,#-32]!
+	mov x29, sp
+	.endm
+
+	comment "subroutine epilogue"
+	.macro gdbasm_leave
+	ldp	x29, x30, [sp],#32
+	ret
+	.endm
+
+	.macro gdbasm_call subr
+	bl \subr
+	.endm
+
+	.macro gdbasm_several_nops
+	nop
+	nop
+	nop
+	nop
+	.endm
+
+	comment "exit (0)"
+	.macro gdbasm_exit0
+	mov x8, #93
+	svc 0
+	.endm
+
+	comment "crt0 startup"
+	.macro gdbasm_startup
+	mov x0, sp
+	.endm
+

gdb/testsuite/gdb.asm/asm-source.exp

@@ -40,6 +40,9 @@ switch -glob -- [istarget] {
     "arm*-*-*" {
         set asm-arch arm
     }
+    "aarch64*-*-*" {
+	set asm-arch aarch64
+    }
     "bfin-*-*" {
         set asm-arch bfin
     }