add mips64 cpu

cpu/BUILD

diff --git a/cpu/BUILD b/cpu/BUILD
index 32f2958..00c2901 100644
--- a/cpu/BUILD
+++ b/cpu/BUILD
@@ -114,3 +114,8 @@
     name = "wasm64",
     constraint_setting = ":cpu",
 )
+
+constraint_value(
+    name = "mips64",
+    constraint_setting = ":cpu",
+)