[cherry-pick swift/release/6.0][clang][headers] Including stddef.h always redefines NULL #9003
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…ways redefines NULL stddef.h always includes __stddef_null.h. This is fine in modules because it's not possible to re-include the pcm, and it's necessary to export the _Builtin_stddef.null submodule. However, without modules it causes NULL to always get redefined which disrupts some C++ code. Rework the inclusion of __stddef_null.h so that with not building with modules it's only included if __need_NULL is set by the includer, or it's the first time stddef.h is being included. rdar://131450006
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@swift-ci test |
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Explanation: This fixes a regression from llvm#90676 where including <stddef.h> multiple times will overwrite the declaration of NULL. This breaks compiling gcc with clang. |
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@swift-ci test llvm |
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LLVM test failures look unrelated. Several |
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stddef.h always includes __stddef_null.h. This is fine in modules because it's not possible to re-include the pcm, and it's necessary to export the _Builtin_stddef.null submodule. However, without modules it causes NULL to always get redefined which disrupts some C++ code. Rework the inclusion of __stddef_null.h so that with not building with modules it's only included if __need_NULL is set by the includer, or it's the first time stddef.h is being included.
rdar://131450006