undef offsetof before defining it in stddef.h

This prevents redefinition warnings by -Wsystem-headers on
OSses where system headers happen to provide a definition of
their own, such as VxWorks.

2022-02-15  Olivier Hainque  <hainque@adacore.com>

gcc/
	* ginclude/stddef.h: #undef offsetof before #define.

diff --git a/gcc/ginclude/stddef.h b/gcc/ginclude/stddef.h
index 3d29213e8f15bd12e33d94c996bb13cc9071a312..2767edf51def4a6121a3c162aac1208b9afbaec1 100644 (file)
--- a/gcc/ginclude/stddef.h
+++ b/gcc/ginclude/stddef.h
@@ -412,6 +412,7 @@ typedef __WINT_TYPE__ wint_t;
 #ifdef _STDDEF_H
 
 /* Offset of member MEMBER in a struct of type TYPE. */
+#undef offsetof                /* in case a system header has defined it. */
 #define offsetof(TYPE, MEMBER) __builtin_offsetof (TYPE, MEMBER)
 
 #if (defined (__STDC_VERSION__) && __STDC_VERSION__ >= 201112L) \