[xray] Ignore -Wc++20-extensions in xray_records.h [NFC]

/data/llvm-project/compiler-rt/lib/xray/../../include/xray/xray_records.h:48:24: error: default member initializer for bit-field is a C++20 extension [
-Werror,-Wc++20-extensions]
  bool ConstantTSC : 1 = false;
                       ^
/data/llvm-project/compiler-rt/lib/xray/../../include/xray/xray_records.h:49:23: error: default member initializer for bit-field is a C++20 extension [
-Werror,-Wc++20-extensions]
  bool NonstopTSC : 1 = false;
                      ^
2 errors generated.