[Binary] Add iterator to the OffloadBinary string maps

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.

Reviewed By: tra

Differential Revision: https://reviews.llvm.org/D127774

llvm/include/llvm/Object/OffloadBinary.h

@@ -59,6 +59,9 @@ enum ImageKind : uint16_t {
 /// 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;
@@ -88,6 +91,11 @@ public:
     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(); }