[Binary] Add iterator to the OffloadBinary string maps

[jhuber6]

Summary

The offload binary contains internally a string map of all the key and
value pairs identified in the binary itself. Normally users query these
values from the getString function, but this makes it difficult to
identify which strings are availible. This patch adds a simple const
iterator range to the offload binary allowing users to iterate through
the strings.

[tra]

llvm/include/llvm/Object/OffloadBinary.h

62–63

Should these be public?

65–66

Do we need these? They are not public and are used in just one place where we could just use StringData.begin()/end() directly.

[jhuber6]

addressing comments.

llvm/include/llvm/Object/OffloadBinary.h

 ///
 /// Many of these could be stored in the same section by the time the linker
 /// sees it so we mark this information with a header. The version is used to
 /// detect ABI stability and the size is used to find other offloading entries
 /// that may exist in the same section. All offsets are given as absolute byte
 /// offsets from the beginning of the file.
 class OffloadBinary : public Binary {
 public:
+  using string_iterator = StringMap<StringRef>::const_iterator;
+  using string_iterator_range = iterator_range<string_iterator>;
+
   /// The offloading metadata that will be serialized to a memory buffer.
   struct OffloadingImage {
     ImageKind TheImageKind;
     OffloadKind TheOffloadKind;
     uint32_t Flags;
     StringMap<StringRef> StringData;
     std::unique_ptr<MemoryBuffer> Image;
   };
 
   /// Attempt to parse the offloading binary stored in \p Data.
public:
   uint64_t getSize() const { return TheHeader->Size; }
 
   StringRef getTriple() const { return getString("triple"); }
   StringRef getArch() const { return getString("arch"); }
   StringRef getImage() const {
     return StringRef(&Buffer[TheEntry->ImageOffset], TheEntry->ImageSize);
   }
 
+  // Iterator over all the key and value pairs in the binary.
+  string_iterator_range strings() const {
+    return string_iterator_range(StringData.begin(), StringData.end());
+  }
+
   StringRef getString(StringRef Key) const { return StringData.lookup(Key); }
 
   static bool classof(const Binary *V) { return V->isOffloadFile(); }
 
 private:
   struct Header {
     uint8_t Magic[4] = {0x10, 0xFF, 0x10, 0xAD}; // 0x10FF10AD magic bytes.
     uint32_t Version = 1;                        // Version identifier.