Add isdefinedglobal builtin

JuliaLang/julia#54999, JuliaLang/julia#56985

Author: mlechu

src/closure_conversion.jl

@@ -337,6 +337,13 @@ function _convert_closures(ctx::ClosureConversionCtx, ex)
         elseif binfo.is_always_defined || is_self_captured(ctx, var)
             # Captured but unboxed vars are always defined
             @ast ctx ex true::K"Bool"
+        elseif kind(var) == K"globalref"
+            # Normal isdefined won't work for globals (#56985)
+            @ast ctx ex [K"call"
+                "isdefinedglobal"::K"core"
+                ctx.mod::K"Value"
+                binfo.name::K"Symbol"
+                false::K"Bool"]
         else
             ex
         end

src/desugaring.jl

@@ -3409,7 +3409,11 @@ function expand_abstract_or_primitive_type(ctx, ex)
         [K"global" name]
         [K"if"
             [K"&&"
-                [K"isdefined" name]
+                [K"call"
+                   "isdefinedglobal"::K"core"
+                   ctx.mod::K"Value"
+                   name=>K"Symbol"
+                   false::K"Bool"]
                 [K"call" "_equiv_typedef"::K"core" name newtype_var]
             ]
             nothing_(ctx, ex)
@@ -3936,7 +3940,10 @@ function expand_struct_def(ctx, ex, docs)
                 [K"=" struct_name newtype_var]
                 [K"call"(supertype) "_setsuper!"::K"core" newtype_var supertype]
                 [K"if"
-                    [K"isdefined" global_struct_name]
+                    [K"call" "isdefinedglobal"::K"core"
+                       ctx.mod::K"Value"
+                       struct_name=>K"Symbol"
+                       false::K"Bool"]
                     [K"if"
                         [K"call" "_equiv_typedef"::K"core" global_struct_name newtype_var]
                         [K"block"