See:  https://github.com/smlnj/smlnj/issues/279

--- llvm-13.0.1.src/include/llvm/Support/Signals.h.orig	2024-12-08 14:34:21.338967469 +0100
+++ llvm-13.0.1.src/include/llvm/Support/Signals.h	2024-12-08 14:32:22.486780827 +0100
@@ -14,6 +14,7 @@
 #ifndef LLVM_SUPPORT_SIGNALS_H
 #define LLVM_SUPPORT_SIGNALS_H
 
+#include <cstdint>
 #include <string>
 
 namespace llvm {