Insert null checks for pointer dereferences when debug assertions are enabled

Similar to how the alignment is already checked, this adds a check
for null pointer dereferences in debug mode. It is implemented similarly
to the alignment check as a MirPass.

This is related to a 2025H1 project goal for better UB checks in debug
mode: rust-lang/rust-project-goals#177.

Author: 1c3t3a

crates/hir-def/src/lang_item.rs

@@ -411,6 +411,7 @@ language_item_table! {
     PanicLocation,           sym::panic_location,      panic_location,             Target::Struct,         GenericRequirement::None;
     PanicImpl,               sym::panic_impl,          panic_impl,                 Target::Fn,             GenericRequirement::None;
     PanicCannotUnwind,       sym::panic_cannot_unwind, panic_cannot_unwind,        Target::Fn,             GenericRequirement::Exact(0);
+    PanicNullPointerDereference, sym::panic_null_pointer_dereference, panic_null_pointer_dereference, Target::Fn, GenericRequirement::None;
     /// libstd panic entry point. Necessary for const eval to be able to catch it
     BeginPanic,              sym::begin_panic,         begin_panic_fn,             Target::Fn,             GenericRequirement::None;
 

crates/intern/src/symbol/symbols.rs

@@ -363,6 +363,7 @@ define_symbols! {
     panic_location,
     panic_misaligned_pointer_dereference,
     panic_nounwind,
+    panic_null_pointer_dereference,
     panic,
     Param,
     parse,