Arm64: arrange for line number emission for .inst

Just like insns encoded the more conventional way these should have line
number info associated with them.

gas/config/tc-aarch64.c

@@ -1982,6 +1982,7 @@ static void
 s_aarch64_inst (int ignored ATTRIBUTE_UNUSED)
 {
   expressionS exp;
+  unsigned n = 0;
 
 #ifdef md_flush_pending_output
   md_flush_pending_output ();
@@ -2020,10 +2021,13 @@ s_aarch64_inst (int ignored ATTRIBUTE_UNUSED)
 	  unsigned int val = exp.X_add_number;
 	  exp.X_add_number = SWAP_32 (val);
 	}
-      emit_expr (&exp, 4);
+      emit_expr (&exp, INSN_SIZE);
+      ++n;
     }
   while (*input_line_pointer++ == ',');
 
+  dwarf2_emit_insn (n * INSN_SIZE);
+
   /* Put terminator back into stream.  */
   input_line_pointer--;
   demand_empty_rest_of_line ();

gas/testsuite/gas/aarch64/inst-directive.d

@@ -6,3 +6,6 @@ Disassembly of section \.text:
 
 0+ <.*>:
    0:	3619194c 	tbz	w12, #3, 2328 <\.text\+0x2328>
+ *[0-9a-f]*:	d503201f 	nop
+ *[0-9a-f]*:	d503201f 	nop
+ *[0-9a-f]*:	d503201f 	nop

gas/testsuite/gas/aarch64/inst-directive.s

@@ -3,3 +3,4 @@
 
 .text
 	.inst	0x3619194c
+	.inst	0xd503201f, 0xd503201f, 0xd503201f

gas/testsuite/gas/aarch64/inst-dwarf.d

@@ -0,0 +1,15 @@
+#as: -gdwarf-2
+#name: Dwarf line number info for .inst
+#objdump: -WL -w
+#source: inst-directive.s
+
+.*:[ 	]+file format .*
+
+Contents of the .debug_line section:
+
+CU: .*/inst-directive.s:
+File name +Line number +Starting address.*
+inst-directive.s +5 +0.*
+inst-directive.s +6 +0x4.*
+inst-directive.s +- +0x10
+#pass