Revert "[lldb][test] TestDataFormatterLibcxxStringSimulator.py: add new padding layout (llvm#108375)"

This reverts commit d5f6e88.

Caused failure on Windows CI. Following test failed:
```
Config=aarch64-C:\Users\tcwg\llvm-worker\lldb-aarch64-windows\build\bin\clang.exe

======================================================================

FAIL: test_r5_c2_ALTERNATE_LAYOUT (TestDataFormatterLibcxxStringSimulator.LibcxxStringDataFormatterSimulatorTestCase.test_r5_c2_ALTERNATE_LAYOUT)

    partial(func, *args, **keywords) - new function with partial application

----------------------------------------------------------------------

Traceback (most recent call last):

  File "C:\Users\tcwg\llvm-worker\lldb-aarch64-windows\llvm-project\lldb\test\API\functionalities\data-formatter\data-formatter-stl\libcxx-simulators\string\TestDataFormatterLibcxxStringSimulator.py", line 23, in _run_test

    self.expect_var_path("longstring", summary='"I am a very long string"')

  File "C:\Users\tcwg\llvm-worker\lldb-aarch64-windows\llvm-project\lldb\packages\Python\lldbsuite\test\lldbtest.py", line 2552, in expect_var_path

    value_check.check_value(self, eval_result, str(eval_result))

  File "C:\Users\tcwg\llvm-worker\lldb-aarch64-windows\llvm-project\lldb\packages\Python\lldbsuite\test\lldbtest.py", line 321, in check_value

    test_base.assertEqual(

AssertionError: '"I am a very long string"' != '""'

- "I am a very long string"

+ ""

 : (std::__lldb::string) longstring = ""

Checking SBValue: (std::__lldb::string) longstring = ""
```

We may need to use `msvc::no_unique_address` around the simulators.

(cherry picked from commit ee4dd14)

Author: Michael137

lldb/test/API/functionalities/data-formatter/data-formatter-stl/libcxx-simulators/string/TestDataFormatterLibcxxStringSimulator.py

@@ -27,7 +27,7 @@ def _run_test(self, defines):
 
 
 for v in [None, "ALTERNATE_LAYOUT"]:
-    for r in range(6):
+    for r in range(5):
         for c in range(3):
             name = "test_r%d_c%d" % (r, c)
             defines = ["REVISION=%d" % r, "COMPRESSED_PAIR_REV=%d" % c]

lldb/test/API/functionalities/data-formatter/data-formatter-stl/libcxx-simulators/string/main.cpp

@@ -20,11 +20,7 @@
 // Pre-D128285 layout.
 #define PACKED_ANON_STRUCT
 #endif
-#if REVISION <= 4
-// Pre-2a1ef74 layout.
-#define NON_STANDARD_PADDING
-#endif
-// REVISION == 5: current layout
+// REVISION == 4: current layout
 
 #ifdef PACKED_ANON_STRUCT
 #define BEGIN_PACKED_ANON_STRUCT struct __attribute__((packed)) {
@@ -38,21 +34,13 @@
 namespace std {
 namespace __lldb {
 
-#ifdef NON_STANDARD_PADDING
 #if defined(ALTERNATE_LAYOUT) && defined(SUBCLASS_PADDING)
 template <class _CharT, size_t = sizeof(_CharT)> struct __padding {
   unsigned char __xx[sizeof(_CharT) - 1];
 };
 
 template <class _CharT> struct __padding<_CharT, 1> {};
 #endif
-#else // !NON_STANDARD_PADDING
-template <size_t _PaddingSize> struct __padding {
-  char __padding_[_PaddingSize];
-};
-
-template <> struct __padding<0> {};
-#endif
 
 template <class _CharT, class _Traits, class _Allocator> class basic_string {
 public:
@@ -89,12 +77,7 @@ template <class _CharT, class _Traits, class _Allocator> class basic_string {
     };
 #else // !SUBCLASS_PADDING
 
-#ifdef NON_STANDARD_PADDING
     unsigned char __padding[sizeof(value_type) - 1];
-#else
-    [[no_unique_address]] __padding<sizeof(value_type) - 1> __padding_;
-#endif
-
 #ifdef BITMASKS
     unsigned char __size_;
 #else // !BITMASKS
@@ -146,26 +129,21 @@ template <class _CharT, class _Traits, class _Allocator> class basic_string {
     union {
 #ifdef BITMASKS
       unsigned char __size_;
-#else  // !BITMASKS
+#else
       struct {
         unsigned char __is_long_ : 1;
         unsigned char __size_ : 7;
       };
-#endif // BITMASKS
+#endif
       value_type __lx;
     };
-#else  // !SHORT_UNION
+#else
     BEGIN_PACKED_ANON_STRUCT
     unsigned char __is_long_ : 1;
     unsigned char __size_ : 7;
     END_PACKED_ANON_STRUCT
-#ifdef NON_STANDARD_PADDING
-    unsigned char __padding[sizeof(value_type) - 1];
-#else  // !NON_STANDARD_PADDING
-    [[no_unique_address]] __padding<sizeof(value_type) - 1> __padding_;
-#endif // NON_STANDARD_PADDING
-
-#endif // SHORT_UNION
+    char __padding_[sizeof(value_type) - 1];
+#endif
     value_type __data_[__min_cap];
   };