[clang] [llvm] Enable fexec-charset option (PR #138895)

[Abhina Sree via cfe-commits]

================
@@ -1814,7 +1851,7 @@ CharLiteralParser::CharLiteralParser(const char *begin, const char *end,
   } else if (tok::utf32_char_constant == Kind) {
     largest_character_for_kind = 0x10FFFF;
   } else {
-    largest_character_for_kind = 0x7Fu;
+    largest_character_for_kind = (Converter == nullptr) ? 0x7Fu : 0xFFu;
----------------
abhina-sree wrote:

It can be if the fexec-charset is unspecified and defaults to UTF-8, in which case the converter will remain a nullptr

https://github.com/llvm/llvm-project/pull/138895