[lldb] Provide a better error message for missing symbols (#89433)

This adds a hint to the missing symbols error message to make it easier
to understand what this means to users.

lldb/source/Expression/IRExecutionUnit.cpp

@@ -431,7 +431,9 @@ void IRExecutionUnit::GetRunnableInfo(Status &error, lldb::addr_t &func_addr,
     }
 
     m_failed_lookups.clear();
-
+    ss.PutCString(
+        "\nHint: The expression tried to call a function that is not present "
+        "in the target, perhaps because it was optimized out by the compiler.");
     error.SetErrorString(ss.GetString());
 
     return;

lldb/test/API/lang/cpp/constructors/TestCppConstructors.py

@@ -47,7 +47,7 @@ def test_constructors(self):
         self.expect(
             "expr ClassWithDeletedDefaultCtor().value",
             error=True,
-            substrs=["Couldn't look up symbols:"],
+            substrs=["Couldn't look up symbols:", "function missing"],
         )
 
     @skipIfWindows  # Can't find operator new.