Revert "Don't expose unavailable cstdio functions."

Broke builders that emit different diagnostics. e.g.:

error: 'warning' diagnostics seen but not expected:
  Line 13: alias declarations are a C++11 extension
  Line 20: alias declarations are a C++11 extension

This reverts commit ff87813715.

libcxx/include/__config

@@ -1545,13 +1545,6 @@ _LIBCPP_FUNC_VIS extern "C" void __sanitizer_annotate_contiguous_container(
 #define _LIBCPP_BUILTIN_CONSTANT_P(x) false
 #endif
 
-// Support for _FILE_OFFSET_BITS=64 landed gradually in Android, so the full set
-// of functions used in cstdio may not be available for low API levels when
-// using 64-bit file offsets on LP32.
-#if defined(__BIONIC__) && defined(__USE_FILE_OFFSET64) && __ANDROID_API__ < 24
-#define _LIBCPP_HAS_NO_FGETPOS_FSETPOS
-#endif
-
 #endif // __cplusplus
 
 #endif // _LIBCPP_CONFIG

libcxx/include/cstdio

@@ -131,13 +131,9 @@ using ::putc;
 using ::ungetc;
 using ::fread;
 using ::fwrite;
-#ifndef _LIBCPP_HAS_NO_FGETPOS_FSETPOS
 using ::fgetpos;
-#endif
 using ::fseek;
-#ifndef _LIBCPP_HAS_NO_FGETPOS_FSETPOS
 using ::fsetpos;
-#endif
 using ::ftell;
 using ::rewind;
 using ::clearerr;

libcxx/test/libcxx/depr/depr.c.headers/no_fgetpos_fsetpos.fail.cpp

@@ -1,25 +0,0 @@
-//===----------------------------------------------------------------------===//
-//
-// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-// See https://llvm.org/LICENSE.txt for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-//
-//===----------------------------------------------------------------------===//
-
-// REQUIRES: verify-support
-
-#include <cstdio>
-
-using T = decltype(::fgetpos);
-#ifdef _LIBCPP_HAS_NO_FGETPOS_FSETPOS
-// expected-error@-2 {{no such thing}}
-#else
-// expected-no-diagnostics
-#endif
-
-using U = decltype(::fsetpos);
-#ifdef _LIBCPP_HAS_NO_FGETPOS_FSETPOS
-// expected-error@-2 {{no such thing}}
-#else
-// expected-no-diagnostics
-#endif

libcxx/test/std/depr/depr.c.headers/stdio_h.pass.cpp

@@ -156,13 +156,9 @@ int main(int, char**)
     static_assert((std::is_same<decltype(ungetc(0,fp)), int>::value), "");
     static_assert((std::is_same<decltype(fread((void*)0,0,0,fp)), size_t>::value), "");
     static_assert((std::is_same<decltype(fwrite((const void*)arr,1,0,fp)), size_t>::value), "");
-#ifndef _LIBCPP_HAS_NO_FGETPOS_FSETPOS
     static_assert((std::is_same<decltype(fgetpos(fp, &fpos)), int>::value), "");
-#endif
     static_assert((std::is_same<decltype(fseek(fp, 0,0)), int>::value), "");
-#ifndef _LIBCPP_HAS_NO_FGETPOS_FSETPOS
     static_assert((std::is_same<decltype(fsetpos(fp, &fpos)), int>::value), "");
-#endif
     static_assert((std::is_same<decltype(ftell(fp)), long>::value), "");
     static_assert((std::is_same<decltype(rewind(fp)), void>::value), "");
     static_assert((std::is_same<decltype(clearerr(fp)), void>::value), "");

libcxx/test/std/input.output/file.streams/c.files/cstdio.pass.cpp

@@ -120,13 +120,9 @@ int main(int, char**)
     static_assert((std::is_same<decltype(std::ungetc(0,fp)), int>::value), "");
     static_assert((std::is_same<decltype(std::fread((void*)0,0,0,fp)), std::size_t>::value), "");
     static_assert((std::is_same<decltype(std::fwrite((const void*)0,0,0,fp)), std::size_t>::value), "");
-#ifndef _LIBCPP_HAS_NO_FGETPOS_FSETPOS
     static_assert((std::is_same<decltype(std::fgetpos(fp, &fpos)), int>::value), "");
-#endif
     static_assert((std::is_same<decltype(std::fseek(fp, 0,0)), int>::value), "");
-#ifndef _LIBCPP_HAS_NO_FGETPOS_FSETPOS
     static_assert((std::is_same<decltype(std::fsetpos(fp, &fpos)), int>::value), "");
-#endif
     static_assert((std::is_same<decltype(std::ftell(fp)), long>::value), "");
     static_assert((std::is_same<decltype(std::rewind(fp)), void>::value), "");
     static_assert((std::is_same<decltype(std::clearerr(fp)), void>::value), "");