[lldb][NFC] Define DWARFDIE::children out-of-line instead of using template magic

As pointed out by David in D103172 (thanks!)

Reviewed By: dblaikie

Differential Revision: https://reviews.llvm.org/D106743

Author: Teemperor

lldb/source/Plugins/SymbolFile/DWARF/DWARFDIE.cpp

@@ -448,3 +448,7 @@ bool DWARFDIE::GetDIENamesAndRanges(
   } else
     return false;
 }
+
+llvm::iterator_range<DWARFDIE::child_iterator> DWARFDIE::children() const {
+  return llvm::make_range(child_iterator(*this), child_iterator());
+}

lldb/source/Plugins/SymbolFile/DWARF/DWARFDIE.h

@@ -90,14 +90,9 @@ class DWARFDIE : public DWARFBaseDIE {
                             int &decl_line, int &decl_column, int &call_file,
                             int &call_line, int &call_column,
                             lldb_private::DWARFExpression *frame_base) const;
+
   /// The range of all the children of this DIE.
-  ///
-  /// This is a template just because child_iterator is not completely defined
-  /// at this point.
-  template <typename T = child_iterator>
-  llvm::iterator_range<T> children() const {
-    return llvm::make_range(T(*this), T());
-  }
+  llvm::iterator_range<child_iterator> children() const;
 };
 
 class DWARFDIE::child_iterator