MFC 307756: Define max_align_t for C11.

libc++'s stddef.h includes an existing definition of max_align_t for
C++11, but it is only defined for C++, not for C.  In addition, GCC and
clang both define an alternate version of max_align_t that uses a
union of multiple types rather than a plain long double as in libc++.
This adds a __max_align_t to <sys/_types.h> that matches the GCC and
clang definition that is mapped to max_align_t in <stddef.h>.

PR:		210890

2 files changed, 13 insertions, 0 deletions

diff --git a/include/stddef.h b/include/stddef.h
index 2c73a2e..99629e0 100644
--- a/include/stddef.h
+++ b/include/stddef.h
@@ -59,6 +59,14 @@ typedef	___wchar_t	wchar_t;
 #endif
 #endif
 
+#if __STDC_VERSION__ >= 201112L || __cplusplus >= 201103L
+#ifndef __CLANG_MAX_ALIGN_T_DEFINED
+typedef	__max_align_t	max_align_t;
+#define __CLANG_MAX_ALIGN_T_DEFINED
+#define __GCC_MAX_ALIGN_T
+#endif
+#endif
+
 #define	offsetof(type, member)	__offsetof(type, member)
 
 #endif /* _STDDEF_H_ */
diff --git a/sys/sys/_types.h b/sys/sys/_types.h
index ffef9d8..8c16c6e 100644
--- a/sys/sys/_types.h
+++ b/sys/sys/_types.h
@@ -99,6 +99,11 @@ typedef	__uint_least32_t __char32_t;
 #define	_CHAR32_T_DECLARED
 #endif
 
+typedef struct {
+	long long __max_align1 __aligned(_Alignof(long long));
+	long double __max_align2 __aligned(_Alignof(long double));
+} __max_align_t;
+
 typedef	__uint32_t	__dev_t;	/* device number */
 
 typedef	__uint32_t	__fixpt_t;	/* fixed point number */