add cstdarg and fix (c)stddef in C89/C++98

Author: ZERICO2005

src/libc/include/stddef.h

@@ -14,12 +14,14 @@ typedef __WCHAR_TYPE__ wchar_t;
 #endif /* __cplusplus */
 #endif /* _WCHAR_T_DEFINED */
 
+#if __STDC_VERSION__ >= 199901L || __cplusplus >= 201103L
 typedef struct {
     long long    __max_align_ll __attribute__((__aligned__(__alignof__(  long long))));
     long double  __max_align_ld __attribute__((__aligned__(__alignof__(long double))));
 #ifdef __FLOAT128__
     __float128 __max_align_f128 __attribute__((__aligned__(__alignof__( __float128))));
 #endif
 } max_align_t;
+#endif /* __STDC_VERSION__ >= 199901L || __cplusplus >= 201103L */
 
 #endif /* _STDDEF_H */

src/libcxx/header_test.cpp

@@ -15,6 +15,7 @@
 #endif // __cplusplus >= 201907L
 #include <csetjmp>
 #include <cstdalign>
+#include <cstdarg>
 #include <cstdbool>
 #include <cstddef>
 #include <cstdint>

src/libcxx/include/cstdarg

@@ -0,0 +1,15 @@
+// -*- C++ -*-
+#ifndef _EZCXX_CSTDARG
+#define _EZCXX_CSTDARG
+
+#include <stdarg.h>
+
+#pragma clang system_header
+
+namespace std {
+
+using ::va_list;
+
+} // namespace std
+
+#endif // _EZCXX_CSTDARG

src/libcxx/include/cstddef

@@ -10,9 +10,13 @@ namespace std {
 
 using ::ptrdiff_t;
 using ::size_t;
+
+#if __cplusplus >= 201103L
 using ::max_align_t;
 using nullptr_t = decltype(nullptr);
+#endif /* __cplusplus >= 201103L */
 
+#if __cplusplus >= 201703L
 enum class byte : unsigned char {};
 
 constexpr byte  operator| (byte __lhs, byte __rhs) noexcept { return byte(char(__lhs) | char(__rhs)); }
@@ -22,6 +26,7 @@ constexpr byte& operator&=(byte& __lhs, byte __rhs) noexcept { return __lhs = __
 constexpr byte  operator^ (byte __lhs, byte __rhs) noexcept { return byte(char(__lhs) ^ char(__rhs)); }
 constexpr byte& operator^=(byte& __lhs, byte __rhs) noexcept { return __lhs = __lhs ^ __rhs; }
 constexpr byte  operator~ (byte __rhs) noexcept { return byte(~char(__rhs)); }
+#endif /* __cplusplus >= 201703L */
 
 } // namespace std