[clang] [dataflow][nfc] Fix u8 string usage with c++20 (PR #84291)

[via cfe-commits]

================
@@ -500,7 +500,7 @@ class HTMLLogger : public Logger {
     for (unsigned I = 0; I < CFG.getNumBlockIDs(); ++I) {
       std::string Name = blockID(I);
       // Rightwards arrow, vertical line
-      char ConvergenceMarker[] = u8"\\n\u2192\u007c";
+      char ConvergenceMarker[] = "\\n\u2192\u007c";
----------------
martinboehme wrote:

Thanks. Will revert and re-land with your suggestion. Sorry for the breakage!

https://github.com/llvm/llvm-project/pull/84291