[NFC][XCOFF][AIX] Rename ControlSections to CsectGroup

[jasonliu]

Summary

The name of ControlSections is not expressive enough to convey what they really are. CsectGroup can better communicate the concept of grouping csects together since they have similar property.

[daltenty]

LGTM

llvm/lib/MC/XCOFFObjectWriter.cpp

struct Section {
   }
 };
 
 class XCOFFObjectWriter : public MCObjectWriter {
   // Type to be used for a container representing a set of csects with
   // (approximately) the same storage mapping class. For example all the csects
   // with a storage mapping class of `xmc_pr` will get placed into the same
   // container.
-  using ControlSections = std::deque<ControlSection>;
+  using CsectGroup = std::deque<ControlSection>;
 
   support::endian::Writer W;
   std::unique_ptr<MCXCOFFObjectTargetWriter> TargetObjectWriter;
   StringTableBuilder Strings;
 
   // The non-empty sections, in the order they will appear in the section header
   // table.
   std::vector<Section *> Sections;
 
   // The Predefined sections.
   Section Text;
   Section BSS;
 
-  // ControlSections. These store the csects which make up different parts of
+  // CsectGroups. These store the csects which make up different parts of
   // the sections. Should have one for each set of csects that get mapped into
   // the same section and get handled in a 'similar' way.
-  ControlSections ProgramCodeCsects;
-  ControlSections BSSCsects;
+  CsectGroup ProgramCodeCsects;
+  CsectGroup BSSCsects;
 
   uint32_t SymbolTableEntryCount = 0;
   uint32_t SymbolTableOffset = 0;
 
   virtual void reset() override;
 
   void executePostLayoutBinding(MCAssembler &, const MCAsmLayout &) override;