Allow creation of default i64 global values

See issue #827.

document/js-api/index.bs

@@ -748,6 +748,7 @@ which can be simultaneously referenced by multiple {{Instance}} objects. Each
 <div algorithm>
     The algorithm <dfn>ToValueType</dfn>(|s|) performs the following steps:
     1. If |s| equals "i32", return [=𝗂𝟥𝟤=].
+    1. If |s| equals "i64", return [=𝗂𝟨𝟦=].
     1. If |s| equals "f32", return [=𝖿𝟥𝟤=].
     1. If |s| equals "f64", return [=𝖿𝟨𝟦=].
     1. Otherwise, throw a {{TypeError}} exception.
@@ -756,6 +757,7 @@ which can be simultaneously referenced by multiple {{Instance}} objects. Each
 <div algorithm>
     The algorithm <dfn>DefaultValue</dfn>(|valuetype|) performs the following steps:
     1. If |valuetype| equals [=𝗂𝟥𝟤=], return [=𝗂𝟥𝟤.𝖼𝗈𝗇𝗌𝗍=] 0.
+    1. If |valuetype| equals [=𝗂𝟨𝟦=], return [=𝗂𝟨𝟦.𝖼𝗈𝗇𝗌𝗍=] 0.
     1. If |valuetype| equals [=𝖿𝟥𝟤=], return [=𝖿𝟥𝟤.𝖼𝗈𝗇𝗌𝗍=] 0.
     1. If |valuetype| equals [=𝖿𝟨𝟦=], return [=𝖿𝟨𝟦.𝖼𝗈𝗇𝗌𝗍=] 0.
     1. Otherwise, throw a {{TypeError}} exception.
@@ -765,6 +767,11 @@ which can be simultaneously referenced by multiple {{Instance}} objects. Each
     The <dfn constructor for="Global">Global(descriptor, v)</dfn> constructor, when invoked, performs the following steps:
     1. Let |mutable| be |descriptor|["mutable"].
     1. Let |valuetype| be [=ToValueType=](|descriptor|["value"]).
+    1. If |v| is undefined,
+       1. let |value| be [=DefaultValue=](|valuetype|).
+    1. Otherwise,
+       1. If |valuetype| is [=𝗂𝟨𝟦=], throw a {{TypeError}} exception.
+       1. Let |value| be [=ToWebAssemblyValue=](|v|, |valuetype|).
     1. If |v| is undefined, let |value| be [=DefaultValue=](|valuetype|); otherwise, let |value| be [=ToWebAssemblyValue=](|v|, |valuetype|).
     1. If |mutable| is true, let |globaltype| be [=var=] |valuetype|; otherwise, let |globaltype| be [=const=] |valuetype|.
     1. Let |store| be the current agent's [=associated store=].