i386: pcmpestr 64-bit sign extension bug

The abs1 function in ops_sse.h only works sorrectly when the result fits
in a signed int. This is fine most of the time because we're only dealing
with byte sized values.

However pcmp_elen helper function uses abs1 to calculate the absolute value
of a cpu register. This incorrectly truncates to 32 bits, and will give
the wrong anser for the most negative value.

Fix by open coding the saturation check before taking the absolute value.

Signed-off-by: Paul Brook <paul@nowt.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

target/i386/ops_sse.h

@@ -2011,25 +2011,23 @@ SSE_HELPER_Q(helper_pcmpgtq, FCMPGTQ)
 
 static inline int pcmp_elen(CPUX86State *env, int reg, uint32_t ctrl)
 {
-    int val;
+    target_long val, limit;
 
     /* Presence of REX.W is indicated by a bit higher than 7 set */
     if (ctrl >> 8) {
-        val = abs1((int64_t)env->regs[reg]);
+        val = (target_long)env->regs[reg];
     } else {
-        val = abs1((int32_t)env->regs[reg]);
+        val = (int32_t)env->regs[reg];
     }
-
     if (ctrl & 1) {
-        if (val > 8) {
-            return 8;
-        }
+        limit = 8;
     } else {
-        if (val > 16) {
-            return 16;
-        }
+        limit = 16;
     }
-    return val;
+    if ((val > limit) || (val < -limit)) {
+        return limit;
+    }
+    return abs1(val);
 }
 
 static inline int pcmp_ilen(Reg *r, uint8_t ctrl)