[lldb][test] Add test-cases for packed structures

Adds test that checks that LLDB correctly infers the
alignment of packed structures. Specifically, the
`InferAlignment` code-path of the `ItaniumRecordLayoutBuilder`
where it assumes that overlapping field offsets imply a
packed structure and thus sets alignment to `1`. See discussion
in #93809.

Also adds two XFAIL-ed tests:
1. where LLDB doesn't correctly infer the alignment of a derived class whose base has
an explicit `DW_AT_alignment. See #73623.
2. where the aforementioned `InferAlignment` kicks in for
   overlapping fields (but in this case incorrectly since
   the structure isn't actually packed).

Author: Michael137

lldb/test/API/lang/cpp/alignas_base_class/TestAlignAsBaseClass.py

@@ -16,3 +16,11 @@ def test(self):
         # Verify specified class alignments.
         self.expect_expr("alignof(B2)", result_value="8")
         self.expect_expr("alignof(EmptyClassAlign8)", result_value="8")
+
+    @no_debug_info_test
+    @expectedFailureAll(bugnumber="https://github.com/llvm/llvm-project/issues/73623")
+    def test(self):
+        self.build()
+        self.dbg.CreateTarget(self.getBuildArtifact("a.out"))
+
+        self.expect_expr("alignof(Derived)", result_value="8")

lldb/test/API/lang/cpp/alignas_base_class/main.cpp

@@ -13,4 +13,10 @@ D d3g;
 struct alignas(8) EmptyClassAlign8 {
 } t;
 
+struct alignas(8) __attribute__((packed)) AlignedAndPackedBase {} foo;
+
+struct Derived : AlignedAndPackedBase {
+} bar;
+static_assert(alignof(Derived) == 8);
+
 int main() {}

lldb/test/Shell/SymbolFile/DWARF/no_unique_address-alignment.cpp

@@ -0,0 +1,25 @@
+// XFAIL: *
+
+// RUN: %clangxx_host -gdwarf -o %t %s
+// RUN: %lldb %t \
+// RUN:   -o "b main" \
+// RUN:   -o "expr alignof(OverlappingFields)" \
+// RUN:   -o "expr sizeof(OverlappingFields)" \
+// RUN:   -o exit | FileCheck %s
+
+// CHECK:      (lldb) expr alignof(OverlappingFields)
+// CHECK-NEXT: ${{.*}} = 4
+// CHECK:      (lldb) expr sizeof(OverlappingFields)
+// CHECK-NEXT: ${{.*}} = 8
+
+struct Empty {};
+
+struct OverlappingFields {
+    char y;
+    [[no_unique_address]] Empty e;
+    int z;
+} g_packed_struct;
+static_assert(alignof(OverlappingFields) == 4);
+static_assert(sizeof(OverlappingFields) == 8);
+
+int main() {}

lldb/test/Shell/SymbolFile/DWARF/packed.cpp

@@ -0,0 +1,36 @@
+// RUN: %clangxx_host -gdwarf -o %t %s
+// RUN: %lldb %t \
+// RUN:   -o "b main" \
+// RUN:   -o "expr alignof(packed)" \
+// RUN:   -o "expr sizeof(packed)" \
+// RUN:   -o "expr alignof(packed_and_aligned)" \
+// RUN:   -o "expr sizeof(packed_and_aligned)" \
+// RUN:   -o exit | FileCheck %s
+
+// CHECK:      (lldb) expr alignof(packed)
+// CHECK-NEXT: ${{.*}} = 1
+// CHECK:      (lldb) expr sizeof(packed)
+// CHECK-NEXT: ${{.*}} = 9
+
+// CHECK:      (lldb) expr alignof(packed_and_aligned)
+// CHECK-NEXT: ${{.*}} = 16
+// CHECK:      (lldb) expr sizeof(packed_and_aligned)
+// CHECK-NEXT: ${{.*}} = 16
+
+struct __attribute__((packed)) packed {
+    int x;
+    char y;
+    int z;
+} g_packed_struct;
+static_assert(alignof(packed) == 1);
+static_assert(sizeof(packed) == 9);
+
+struct __attribute__((packed, aligned(16))) packed_and_aligned {
+    int x;
+    char y;
+    int z;
+} g_packed_and_aligned_struct;
+static_assert(alignof(packed_and_aligned) == 16);
+static_assert(sizeof(packed_and_aligned) == 16);
+
+int main() {}