MIPS16/GAS: Reject instructions that end with a dot

Fix a regression from commit 3fb4970943 ("MIPS16/GAS: Fix forced size
suffixes with argumentless instructions") and reject MIPS16 instructions
that end with a dot and no forced size suffix following, e.g.:

$ cat test.s
	.set	mips16
foo:
	break.
	entry.
	addiu.	$2, 0x7fff
	addiu.	$3, $2, 0
	.align	8, 0
$ as -32 -o test.o test.s
$ objdump -d test.o

test.o:     file format elf32-tradbigmips

Disassembly of section .text:

00000000 <foo>:
   0:	e805      	break
   2:	e809      	entry
   4:	f7ef 4a1f 	addiu	v0,32767
   8:	4260      	addiu	v1,v0,0
	...
$

Add a test accordingly, also verifying invalid forced size suffixes.

gas/config/tc-mips.c

@@ -14416,10 +14416,13 @@ mips16_ip (char *str, struct mips_cl_insn *insn)
 	  l = 4;
 	  s++;
 	}
-      if (*s == '\0')
-	break;
-      else if (is_whitespace (*s++))
-	break;
+      if (l != 0)
+	{
+	  if (*s == '\0')
+	    break;
+	  else if (is_whitespace (*s++))
+	    break;
+	}
       set_insn_error (0, _("unrecognized opcode"));
       return;
     }

gas/testsuite/gas/mips/mips.exp

@@ -1523,6 +1523,8 @@ if { [istarget mips*-*-vxworks*] } {
     run_dump_test "mips16-sprel-swap"
     run_dump_test "mips16-sdrasp"
     run_dump_test "mips16-insn-length-noargs"
+    run_dump_test_arches "mips16-insn-length-bad" \
+					[mips_arch_list_matching mips16-32]
 
     run_dump_test "mips16-branch-unextended-1"
     run_dump_test "mips16-branch-unextended-2"

gas/testsuite/gas/mips/mips16-insn-length-bad.d

@@ -0,0 +1,3 @@
+#as: -32
+#name: MIPS16 bad instruction size override
+#error_output: mips16-insn-length-bad.l

gas/testsuite/gas/mips/mips16-insn-length-bad.l

@@ -0,0 +1,11 @@
+.*: Assembler messages:
+.*:3: Error: unrecognized opcode `break\.'
+.*:4: Error: unrecognized opcode `entry\.'
+.*:5: Error: unrecognized opcode `addiu\. \$2,0x7fff'
+.*:6: Error: unrecognized opcode `addiu\. \$3,\$2,0'
+.*:7: Error: unrecognized opcode `exit\.ex'
+.*:8: Error: unrecognized opcode `exit\.tx'
+.*:9: Error: unrecognized opcode `nop\.ey'
+.*:10: Error: unrecognized opcode `nop\.ty'
+.*:11: Error: unrecognized opcode `li\.ez \$2,0'
+.*:12: Error: unrecognized opcode `li\.tz \$2,0'

gas/testsuite/gas/mips/mips16-insn-length-bad.s

@@ -0,0 +1,16 @@
+	.set	mips16
+foo:
+	break.
+	entry.
+	addiu.	$2, 0x7fff
+	addiu.	$3, $2, 0
+	exit.ex
+	exit.tx
+	nop.ey
+	nop.ty
+	li.ez	$2, 0
+	li.tz	$2, 0
+
+# Force some (non-delay-slot) zero bytes, to make 'objdump' print ...
+	.align	4, 0
+	.space	16