Fix compilation on older systems

Cherry-pick upstream commit f97ca48b1cbbf5da065e94271cb3af4f1c907dd4.

Fixes https://bugs.llvm.org/show_bug.cgi?id=47896

libsanitizer/sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cpp

@@ -486,6 +486,10 @@ typedef user_regs_struct regs_struct;
 #define REG_SP rsp
 #endif
 #define ARCH_IOVEC_FOR_GETREGSET
+// Support ptrace extensions even when compiled without required kernel support
+#ifndef NT_X86_XSTATE
+#define NT_X86_XSTATE 0x202
+#endif
 // Compiler may use FP registers to store pointers.
 static constexpr uptr kExtraRegs[] = {NT_X86_XSTATE, NT_FPREGSET};