Use the initializer Expr that is a child of the constructor now that CXXDefaultInitExprs may be copied in the AST.

This fixes a crash that I believe did not exist before llvm/llvm-project#91879. The CXXDefaultInitExpr that is the in-class member initializer is now not the same object that is referenced through the constructor's initializers, so we could no longer retrieve the correct environment values for the expressions involved. We need to use the object referenced by the constructor's initializers.

The minimal crash repro I could find still needed `#include <assert.h>`, so isn't an option for unit tests in collect_evidence_test.cc:

```cpp
#include <assert.h>

#include <memory>

int* g;

class C {
  C() {}

  std::unique_ptr<int, void (*)(int*)> field_{
      g, [](int*) { __assert_fail("", __builtin_FILE(), 0, ""); }};
};
```

PiperOrigin-RevId: 654006679
Change-Id: If4b8455132ae1b637be3544e15e63bcdf962772b

Author: Googler

bazel/llvm.bzl

@@ -53,7 +53,7 @@ def _llvm_loader_repository(repository_ctx):
             executable = False,
         )
 
-LLVM_COMMIT_SHA = "5ff3ff33ff930e4ec49da7910612d8a41eb068cb"
+LLVM_COMMIT_SHA = "dd7d81ea49bf39e1d69bbb84bd3f31bd95519369"
 
 def llvm_loader_repository_dependencies():
     # This *declares* the dependency, but it won't actually be *downloaded* unless it's used.

nullability/inference/collect_evidence.cc

@@ -433,6 +433,9 @@ static bool isOrIsConstructedFromNullPointerConstant(
       Expr::NPCK_NotNull) {
     return true;
   }
+  if (auto *DefaultInit = dyn_cast<CXXDefaultInitExpr>(E)) {
+    E = DefaultInit->getExpr();
+  }
   const Expr *SubExpr = &dataflow::ignoreCFGOmittedNodes(*E);
   if (auto *MaterializeTempExpr = dyn_cast<MaterializeTemporaryExpr>(SubExpr)) {
     SubExpr = MaterializeTempExpr->getSubExpr();
@@ -1165,14 +1168,11 @@ class DefinitionEvidenceCollector {
     // underlying CXXConstructExpr, so we don't need to handle those, only the
     // member initializers.
     const FieldDecl *Field = Initializer->getAnyMember();
-    if (Field == nullptr) return;
-    if (InferableSlots.empty()) return;
-    bool IsDefaultInitializer = Initializer->isInClassMemberInitializer();
-    const Expr *InitExpr = IsDefaultInitializer ? Field->getInClassInitializer()
-                                                : Initializer->getInit();
-
-    if (!isSupportedPointerType(Field->getType())) return;
+    if (Field == nullptr || InferableSlots.empty() ||
+        !isSupportedPointerType(Field->getType()))
+      return;
 
+    bool IsDefaultInitializer = Initializer->isInClassMemberInitializer();
     if (isSupportedSmartPointerType(Field->getType()) &&
         !IsDefaultInitializer && !Initializer->isWritten()) {
       // We skip unwritten non-default member initializers for smart pointer
@@ -1183,6 +1183,7 @@ class DefinitionEvidenceCollector {
       return;
     }
 
+    const Expr *InitExpr = Initializer->getInit();
     bool NullptrDefaultInit =
         IsDefaultInitializer && isOrIsConstructedFromNullPointerConstant(
                                     InitExpr, Field->getASTContext());