[clang] [compiler-rt] [profile] Add `%b` `LLVM_PROFILE_FILE` option for binary ID (PR #123963)

[David Li via cfe-commits]

================
@@ -855,6 +856,15 @@ static int parseFilenamePattern(const char *FilenamePat,
                     FilenamePat);
           return -1;
         }
+      } else if (FilenamePat[I] == 'b') {
+        if (!NumBinaryIds++) {
+          if (__llvm_write_binary_ids(NULL) <= 0) {
----------------
david-xl wrote:

Add a code comment to indicate it reads the size of the binary ids.

https://github.com/llvm/llvm-project/pull/123963