fixes isLocalVarSym; an implicit global is a global nonetheless

[ringabout]

ref #20812

The definition of isLocalVarSym is not correct. I found it when I was debugging #21024. I tried to reuse this function, but it gave surprising results.

For a global variable, it doesn't need both sfGlobal and sfPure flags which indicates it is an explicit global variable because it can be an implicit global variable without a sfPure flag. I expect this function identifies all global variables. So I change its definition.

It should still stand correct for tests in #20812 because the previous PR used a guard statement even it was based on a wrong requirement.

  if {sfGlobal, sfPure} <= v.flags:
    globalVarInitCheck(c, def)

[bung87]

all the code writen there don't expect implicit global variable and only used for globalVarInitCheck, your patch #21024 widen its useage.

[Araq]

Why is it not sfGlobal in v.flags then?

[bung87]

it consistent with compiler/injectdestructors.nim

if {sfGlobal, sfPure} <= v.sym.flags or sfGlobal in v.sym.flags and s.parent == nil: 
  c.graph.globalDestructors.add c.genDestroy(v)

and variables are really declared in global scope.

[github-actions]

Thanks for your hard work on this PR!
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