[libcxx] Direct support for Fuchsia

[phosek]

Summary

Fuchsia's libc was forked from musl, but has evolved sufficiently since then so it no longer makes sense to pretend it's musl. This change implements direct support for Fuchsia rather than piggybacking on musl support.

[EricWF]

LGTM minus inline comments.

include/__locale

44 ↗

(On Diff #94933)

This #endif comment is no longer correct. Please remove it as part of this change.

include/support/fuchsia/xlocale.h

14 ↗

(On Diff #94933)

I don't see the need for this guard, since the header should never be included outside of a Fuchsia environment.
If anything it should read:

#if !defined(__Fuchsia__)
#error Fuchsia specific header incorrectly included
#endif

[phosek]

include/support/fuchsia/xlocale.h

14 ↗

(On Diff #94933)

I was following the pattern used by Android and Newlib, but I'm happy to remove this if you prefer?

libcxx/trunk/include/__config

 // CloudABI is intended for running networked services. Processes do not
 // have standard input and output channels.
 #ifdef __CloudABI__
 #define _LIBCPP_HAS_NO_STDIN
 #define _LIBCPP_HAS_NO_STDOUT
 #endif
 
 #if defined(__BIONIC__) || defined(__CloudABI__) ||                            \
-    defined(_LIBCPP_HAS_MUSL_LIBC)
+    defined(__Fuchsia__) || defined(_LIBCPP_HAS_MUSL_LIBC)
 #define _LIBCPP_PROVIDES_DEFAULT_RUNE_TABLE
 #endif
 
 // Thread-unsafe functions such as strtok() and localtime()
 // are not available.
 #ifdef __CloudABI__
 #define _LIBCPP_HAS_NO_THREAD_UNSAFE_C_FUNCTIONS
 #endif

libcxx/trunk/include/__locale

 #elif defined(__sun__)
 # include <xlocale.h>
 # include <support/solaris/xlocale.h>
 #elif defined(_NEWLIB_VERSION)
 # include <support/newlib/xlocale.h>
 #elif (defined(__GLIBC__) || defined(__APPLE__)      || defined(__FreeBSD__) \
     || defined(__EMSCRIPTEN__) || defined(__IBMCPP__))
 # include <xlocale.h>
+#elif defined(__Fuchsia__)
+# include <support/fuchsia/xlocale.h>
 #elif defined(_LIBCPP_HAS_MUSL_LIBC)
 # include <support/musl/xlocale.h>
-#endif // __GLIBC__ || __APPLE__ || __FreeBSD__ || __sun__ || __EMSCRIPTEN__ || __IBMCPP__
+#endif
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #pragma GCC system_header
 #endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 class _LIBCPP_TYPE_VIS locale;

libcxx/trunk/include/support/fuchsia/xlocale.h

+// -*- C++ -*-
+//===------------------- support/fuchsia/xlocale.h ------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP_SUPPORT_FUCHSIA_XLOCALE_H
+#define _LIBCPP_SUPPORT_FUCHSIA_XLOCALE_H
+
+#if defined(__Fuchsia__)
+
+#include <cstdlib>
+#include <cwchar>
+#include <support/xlocale/__posix_l_fallback.h>
+#include <support/xlocale/__strtonum_fallback.h>
+
+#endif // defined(__Fuchsia__)
+
+#endif // _LIBCPP_SUPPORT_FUCHSIA_XLOCALE_H