tcg: Add muluh and mulsh opcodes

Use them in places where mulu2 and muls2 are used.
Optimize mulx2 with dead low part to mulxh.

Reviewed-by: Aurelien Jarno <aurelien@aurel32.net>
Signed-off-by: Richard Henderson <rth@twiddle.net>
diff --git a/tcg/tcg.h b/tcg/tcg.h
index f3f9889..3f869dd 100644
--- a/tcg/tcg.h
+++ b/tcg/tcg.h
@@ -85,6 +85,8 @@
 #define TCG_TARGET_HAS_sub2_i64         0
 #define TCG_TARGET_HAS_mulu2_i64        0
 #define TCG_TARGET_HAS_muls2_i64        0
+#define TCG_TARGET_HAS_muluh_i64        0
+#define TCG_TARGET_HAS_mulsh_i64        0
 /* Turn some undef macros into true macros.  */
 #define TCG_TARGET_HAS_add2_i32         1
 #define TCG_TARGET_HAS_sub2_i32         1