[lld] [lld][macho] Support order cstrings with -order_file_cstring (PR #140307)

[Ellis Hoag via llvm-commits]

================
@@ -388,3 +388,74 @@ macho::PriorityBuilder::buildInputSectionPriorities() {
 
   return sectionPriorities;
 }
+
+void macho::PriorityBuilder::parseOrderFileCString(StringRef path) {
+  std::optional<MemoryBufferRef> buffer = readFile(path);
+  if (!buffer) {
+    error("Could not read cstring order file at " + path);
+    return;
+  }
+  MemoryBufferRef mbref = *buffer;
+  int priority = std::numeric_limits<int>::min();
+  for (StringRef line : args::getLines(mbref)) {
+    if (line.empty())
+      continue;
+    uint32_t hash = 0;
+    if (!to_integer(line, hash))
+      continue;
+    auto it = cStringPriorities.find(hash);
+    if (it == cStringPriorities.end())
+      cStringPriorities[hash] = ++priority;
----------------
ellishg wrote:

@alx32 if we want to use `try_emplace()` we can do this change if we are ok with setting the priority first and then incrementing
```suggestion
    auto [it, wasInserted] = cStringPriorities.try_emplace(hash, priority);
    if (wasInserted)
      ++priority;
```

https://github.com/llvm/llvm-project/pull/140307