x86: Warn .insn instruction with length > 15 bytes

Change .insn instruction with length > 15 bytes from error to warning.

	PR gas/31323
	* config/tc-i386.c (output_insn): Issue a warning when .insn
	instruction length exceeds the limit of 15 bytes.
	* testsuite/gas/i386/oversized64.s: Add a test for .insn
	* testsuite/gas/i386/oversized64.l: Updated.

gas/config/tc-i386.c

@@ -11780,8 +11780,14 @@ output_insn (const struct last_insn *last_insn)
 	{
 	  j = encoding_length (insn_start_frag, insn_start_off, frag_more (0));
 	  if (j > 15)
-	    as_bad (_("instruction length of %u bytes exceeds the limit of 15"),
-		    j);
+	    {
+	      if (dot_insn ())
+		as_warn (_("instruction length of %u bytes exceeds the limit of 15"),
+			j);
+	      else
+		as_bad (_("instruction length of %u bytes exceeds the limit of 15"),
+			j);
+	    }
 	  else if (fragP)
 	    {
 	      /* NB: Don't add prefix with GOTPC relocation since

gas/testsuite/gas/i386/oversized64.l

@@ -4,6 +4,7 @@
 .*:7: Error: instruction length.*
 .*:9: Error: instruction length.*
 .*:10: Error: instruction length.*
+.*:13: Warning: instruction length.*
 GAS LISTING .*
 
 
@@ -37,4 +38,11 @@ GAS LISTING .*
 [ 	]*10[ 	]+48812CC5[ 	]*
 [ 	]*10[ 	]+00000000[ 	]*
 [ 	]*10[ 	]+44332211[ 	]*
+[ 	]*11[ 	]+
+[ 	]*12[ 	]+\.att_syntax prefix
+[ 	]*13[ 	]+\?\?\?\? 6762F1FC[ 	]+.insn EVEX.L0.0f 12/0, \$0x11223344,\(,%eax,8\),%rax
+\*\*\*\*  Warning: instruction length of 16 bytes exceeds the limit of 15
+[ 	]*13[ 	]+080C04C5[ 	]*
+[ 	]*13[ 	]+00000000[ 	]*
+[ 	]*13[ 	]+44332211[ 	]*
 #pass

gas/testsuite/gas/i386/oversized64.s

@@ -8,3 +8,6 @@ long64:
 
 	xacquire lock add qword ptr gs:[eax*8], 0x11223344
 	xrelease lock sub qword ptr gs:[eax*8], 0x11223344
+
+	.att_syntax prefix
+	.insn EVEX.L0.0f 12/0, $0x11223344,(,%eax,8),%rax