tcg/i386: Conditionalize tcg_out_extu_i32_i64

Since TCG_TYPE_I32 values are kept zero-extended in registers, via
omission of the REXW bit, we need not extend if the register matches.
This is already relied upon by qemu_{ld,st}.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

tcg/i386/tcg-target.c.inc

@@ -1315,7 +1315,9 @@ static void tcg_out_exts_i32_i64(TCGContext *s, TCGReg dest, TCGReg src)
 
 static void tcg_out_extu_i32_i64(TCGContext *s, TCGReg dest, TCGReg src)
 {
-    tcg_out_ext32u(s, dest, src);
+    if (dest != src) {
+        tcg_out_ext32u(s, dest, src);
+    }
 }
 
 static void tcg_out_extrl_i64_i32(TCGContext *s, TCGReg dest, TCGReg src)