cbuilder: add array vars, use for openarray init (#24324)

The remaining followup from #24259. A body for building the type doesn't
seem necessary here since the types with array fields are generally
atomic/already built from `getTypeDescAux`.

compiler/cbuilderdecls.nim

@@ -54,6 +54,32 @@ template addVarWithTypeAndInitializer(builder: var Builder, kind: VarKind = Loca
   initializerBody
   builder.add(";\n")
 
+proc addArrayVar(builder: var Builder, kind: VarKind = Local, name: string, elementType: Snippet, len: int, initializer: Snippet = "") =
+  ## adds an array variable declaration to the builder
+  builder.addVarHeader(kind)
+  builder.add(elementType)
+  builder.add(" ")
+  builder.add(name)
+  builder.add("[")
+  builder.addInt(len)
+  builder.add("]")
+  if initializer.len != 0:
+    builder.add(" = ")
+    builder.add(initializer)
+  builder.add(";\n")
+
+template addArrayVarWithInitializer(builder: var Builder, kind: VarKind = Local, name: string, elementType: Snippet, len: int, body: typed) =
+  ## adds an array variable declaration to the builder with the initializer built according to `body`
+  builder.addVarHeader(kind)
+  builder.add(elementType)
+  builder.add(" ")
+  builder.add(name)
+  builder.add("[")
+  builder.addInt(len)
+  builder.add("] = ")
+  body
+  builder.add(";\n")
+
 template addTypedef(builder: var Builder, name: string, typeBody: typed) =
   ## adds a typedef declaration to the builder with name `name` and type as
   ## built in `typeBody`

compiler/ccgexprs.nim

@@ -3524,16 +3524,15 @@ proc genBracedInit(p: BProc, n: PNode; isConst: bool; optionalType: PType; resul
       if n.kind != nkBracket:
         internalError(p.config, n.info, "const openArray expression is not an array construction")
 
-      var data = newRopeAppender()
-      genConstSimpleList(p, n, isConst, data)
-
       let payload = getTempName(p.module)
       let ctype = getTypeDesc(p.module, typ.elementType)
       let arrLen = n.len
-      appcg(p.module, cfsStrData,
-        "static $5 $1 $3[$2] = $4;$n", [
-        ctype, arrLen, payload, data,
-        if isConst: "const" else: ""])
+      var data = newBuilder("")
+      data.addArrayVarWithInitializer(
+          kind = if isConst: AlwaysConst else: Global,
+          name = payload, elementType = ctype, len = arrLen):
+        genConstSimpleList(p, n, isConst, data)
+      p.module.s[cfsStrData].add(data)
       var openArrInit: StructInitializer
       result.addStructInitializer(openArrInit, kind = siOrderedStruct):
         result.addField(openArrInit, name = "Field0"):