Fix stdin/stdout/stderr for pre-M.

This wasn't an array of pointers, it was an array of structs.
Unfortunately we need a complete type to index into the struct for
stdin/stdout/stderr, so add a phony struct that matches the size and
alignment of `struct __sFILE`. This property is guaranteed by the
static_asserts in libc/bionic/struct_file_test.cpp.

Test: mma
Bug: http://b/30465923
Change-Id: I8ce851dd64a261703bb44f9b5cd23b7caff4dd68

libc/include/bits/struct_file.h

@@ -0,0 +1,46 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#ifndef BITS_FILE_H
+#define BITS_FILE_H
+
+#include <sys/cdefs.h>
+
+__BEGIN_DECLS
+
+struct __sFILE {
+#if defined(__LP64__)
+  char __private[152];
+#else
+  char __private[84];
+#endif
+} __attribute__((aligned(sizeof(void*))));
+
+__END_DECLS
+
+#endif /* BITS_FILE_H */

libc/include/stdio.h

@@ -49,6 +49,10 @@
 
 #include <bits/seek_constants.h>
 
+#if __ANDROID_API__ <= 23
+#include <bits/struct_file.h>
+#endif
+
 __BEGIN_DECLS
 
 #if defined(__clang__)
@@ -73,11 +77,11 @@ extern FILE* stderr __INTRODUCED_IN(23);
 #define stderr stderr
 #else
 /* Before M the actual symbols for stdin and friends had different names. */
-extern FILE* __sF[] __REMOVED_IN(23);
+extern FILE __sF[] __REMOVED_IN(23);
 
-#define stdin __sF[0]
-#define stdout __sF[1]
-#define stderr __sF[2]
+#define stdin (&__sF[0])
+#define stdout (&__sF[1])
+#define stderr (&__sF[2])
 #endif
 
 /*

libc/stdio/stdio.cpp

@@ -848,3 +848,16 @@ int wprintf(const wchar_t* fmt, ...) {
 int wscanf(const wchar_t* fmt, ...) {
   PRINTF_IMPL(vfwscanf(stdin, fmt, ap));
 }
+
+namespace {
+
+namespace phony {
+#include <bits/struct_file.h>
+}
+
+static_assert(sizeof(::__sFILE) == sizeof(phony::__sFILE),
+              "size mismatch between `struct __sFILE` implementation and public stub");
+static_assert(alignof(::__sFILE) == alignof(phony::__sFILE),
+              "alignment mismatch between `struct __sFILE` implementation and public stub");
+
+}