make FILE a complete type for pre-C11 standard profiles

C11 removed the requirement that FILE be a complete type, which was
deemed erroneous, as part of the changes introduced by N1439 regarding
completeness of types (see footnote 6 for specific mention of FILE).
however the current version of POSIX is still based on C99 and
incorporates the old requirement that FILE be a complete type.

expose an arbitrary, useless complete type definition because the
actual object used to represent FILE streams cannot be public/ABI.

thanks to commit 13d1afa46f, we now have
a framework for suppressing the public complete-type definition of FILE
when stdio.h is included internally, so that a different internal
definition can be provided. this is perfectly well-defined, since the
same struct tag can refer to different types in different translation
units. it would be a problem if the implementation were accessing the
application's FILE objects or vice versa, but either would be
undefined behavior.

include/alltypes.h.in

@@ -57,6 +57,7 @@ TYPEDEF struct { unsigned __attr; } pthread_condattr_t;
 TYPEDEF struct { unsigned __attr; } pthread_barrierattr_t;
 TYPEDEF struct { unsigned __attr[2]; } pthread_rwlockattr_t;
 
+STRUCT _IO_FILE { char __x; };
 TYPEDEF struct _IO_FILE FILE;
 
 TYPEDEF struct __mbstate_t { unsigned __opaque1, __opaque2; } mbstate_t;

include/stdio.h

@@ -11,6 +11,10 @@ extern "C" {
 #define __NEED___isoc_va_list
 #define __NEED_size_t
 
+#if __STDC_VERSION__ < 201112L
+#define __NEED_struct__IO_FILE
+#endif
+
 #if defined(_POSIX_SOURCE) || defined(_POSIX_C_SOURCE) \
  || defined(_XOPEN_SOURCE) || defined(_GNU_SOURCE) \
  || defined(_BSD_SOURCE)

include/wchar.h

@@ -14,6 +14,10 @@ extern "C" {
 #define __NEED_wint_t
 #define __NEED_mbstate_t
 
+#if __STDC_VERSION__ < 201112L
+#define __NEED_struct__IO_FILE
+#endif
+
 #if defined(_POSIX_SOURCE) || defined(_POSIX_C_SOURCE) \
  || defined(_XOPEN_SOURCE) || defined(_GNU_SOURCE) || defined(_BSD_SOURCE)
 #define __NEED_locale_t

src/include/stdio.h

@@ -1,6 +1,8 @@
 #ifndef STDIO_H
 #define STDIO_H
 
+#define __DEFINED_struct__IO_FILE
+
 #include "../../include/stdio.h"
 
 #undef stdin

src/include/wchar.h

@@ -0,0 +1,9 @@
+#ifndef WCHAR_H
+#define WCHAR_H
+
+#define __DEFINED_struct__IO_FILE
+
+#include "../../include/wchar.h"
+
+#endif
+