Revert "Merge pull request swiftlang#7619 from ian-twilightcoder/cstdlib-modules"

This reverts commit 1a1fb4b, reversing
changes made to c58c369.

Author: ian-twilightcoder

clang/lib/Basic/Module.cpp

@@ -308,7 +308,8 @@ bool Module::directlyUses(const Module *Requested) {
   // Anyone is allowed to use our builtin stdarg.h and stddef.h and their
   // accompanying modules.
   if (Requested->getTopLevelModuleName() == "_Builtin_stdarg" ||
-      Requested->getTopLevelModuleName() == "_Builtin_stddef")
+      Requested->getTopLevelModuleName() == "_Builtin_stddef" ||
+      (!Requested->Parent && Requested->Name == "_Builtin_stddef_max_align_t"))
     return true;
 
   if (NoUndeclaredIncludes)

clang/lib/Headers/__stddef_max_align_t.h

@@ -1,4 +1,4 @@
-/*===---- __stddef_max_align_t.h - Definition of max_align_t ---------------===
+/*===---- __stddef_max_align_t.h - Definition of max_align_t for modules ---===
  *
  * Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
  * See https://llvm.org/LICENSE.txt for license information.

clang/lib/Headers/__stddef_null.h

@@ -7,15 +7,7 @@
  *===-----------------------------------------------------------------------===
  */
 
-#if !defined(NULL) || !__has_feature(modules)
-
-/* linux/stddef.h will define NULL to 0. glibc (and other) headers then define
- * __need_NULL and rely on stddef.h to redefine NULL to the correct value again.
- * Modules don't support redefining macros like that, but support that pattern
- * in the non-modules case.
- */
 #undef NULL
-
 #ifdef __cplusplus
 #if !defined(__MINGW32__) && !defined(_MSC_VER)
 #define NULL __null
@@ -25,5 +17,3 @@
 #else
 #define NULL ((void *)0)
 #endif
-
-#endif

clang/lib/Headers/__stddef_nullptr_t.h

@@ -7,18 +7,19 @@
  *===-----------------------------------------------------------------------===
  */
 
-#ifndef _NULLPTR_T
+#if !defined(_NULLPTR_T) || __has_feature(modules)
+/* Always define nullptr_t when modules are available. */
+#if !__has_feature(modules)
 #define _NULLPTR_T
-
+#endif
 #ifdef __cplusplus
 #if defined(_MSC_EXTENSIONS) && defined(_NATIVE_NULLPTR_SUPPORTED)
 namespace std {
 typedef decltype(nullptr) nullptr_t;
 }
 using ::std::nullptr_t;
 #endif
-#elif defined(__STDC_VERSION__) && __STDC_VERSION__ >= 202311L
+#else
 typedef typeof(nullptr) nullptr_t;
 #endif
-
 #endif

clang/lib/Headers/__stddef_offsetof.h

@@ -7,6 +7,7 @@
  *===-----------------------------------------------------------------------===
  */
 
-#ifndef offsetof
+#if !defined(offsetof) || __has_feature(modules)
+/* Always define offsetof when modules are available. */
 #define offsetof(t, d) __builtin_offsetof(t, d)
 #endif

clang/lib/Headers/__stddef_ptrdiff_t.h

@@ -7,9 +7,10 @@
  *===-----------------------------------------------------------------------===
  */
 
-#ifndef _PTRDIFF_T
+#if !defined(_PTRDIFF_T) || __has_feature(modules)
+/* Always define ptrdiff_t when modules are available. */
+#if !__has_feature(modules)
 #define _PTRDIFF_T
-
+#endif
 typedef __PTRDIFF_TYPE__ ptrdiff_t;
-
 #endif

clang/lib/Headers/__stddef_rsize_t.h

@@ -7,9 +7,10 @@
  *===-----------------------------------------------------------------------===
  */
 
-#ifndef _RSIZE_T
+#if !defined(_RSIZE_T) || __has_feature(modules)
+/* Always define rsize_t when modules are available. */
+#if !__has_feature(modules)
 #define _RSIZE_T
-
+#endif
 typedef __SIZE_TYPE__ rsize_t;
-
 #endif

clang/lib/Headers/__stddef_size_t.h

@@ -7,9 +7,10 @@
  *===-----------------------------------------------------------------------===
  */
 
-#ifndef _SIZE_T
+#if !defined(_SIZE_T) || __has_feature(modules)
+/* Always define size_t when modules are available. */
+#if !__has_feature(modules)
 #define _SIZE_T
-
+#endif
 typedef __SIZE_TYPE__ size_t;
-
 #endif

clang/lib/Headers/__stddef_unreachable.h

@@ -7,6 +7,7 @@
  *===-----------------------------------------------------------------------===
  */
 
-#ifndef unreachable
+#if !defined(unreachable) || __has_feature(modules)
+/* Always define unreachable when modules are available. */
 #define unreachable() __builtin_unreachable()
 #endif

clang/lib/Headers/__stddef_wchar_t.h

@@ -8,16 +8,14 @@
  */
 
 #if !defined(__cplusplus) || (defined(_MSC_VER) && !_NATIVE_WCHAR_T_DEFINED)
-
-#ifndef _WCHAR_T
+/* Always define wchar_t when modules are available. */
+#if !defined(_WCHAR_T) || __has_feature(modules)
+#if !__has_feature(modules)
 #define _WCHAR_T
-
-#ifdef _MSC_EXTENSIONS
+#if defined(_MSC_EXTENSIONS)
 #define _WCHAR_T_DEFINED
 #endif
-
+#endif
 typedef __WCHAR_TYPE__ wchar_t;
-
 #endif
-
 #endif