assemble: defer MERR_OPSIZEMISSING

In order for the machinery that deduces memory operand sizes when they
are not provided to work correctly, we need to make sure that
MERR_OPSIZEMISSING is only issued by matches() as the last resort;
that way all other error conditions will have been filtered out and we
know at the very end if we have exactly one option left.

This is a partial revert of cd26fccab4,
but does not affect the functionality introduced by that patch.

Reported-by: Cyrill Gorcunov <gorcunov@gmail.com>
Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>

asm/assemble.c

@@ -2170,6 +2170,7 @@ static enum match_result matches(const struct itemplate *itemp,
                                  insn *instruction, int bits)
 {
     opflags_t size[MAX_OPERANDS], asize;
+    bool opsizemissing = false;
     int i, oprs;
 
     /*
@@ -2347,7 +2348,7 @@ static enum match_result matches(const struct itemplate *itemp,
                      * so "missing operand size" for a register should be
                      * considered a wildcard match rather than an error.
                      */
-                    return MERR_OPSIZEMISSING;
+                    opsizemissing = true;
                 }
             } else if (is_broadcast &&
                        (brcast_num !=
@@ -2363,6 +2364,9 @@ static enum match_result matches(const struct itemplate *itemp,
         }
     }
 
+    if (opsizemissing)
+        return MERR_OPSIZEMISSING;
+
     /*
      * Check operand sizes
      */