[libcxx] Port to NuttX (https://nuttx.apache.org) RTOS

Since NuttX conform to POSIX standard, the code need to add is very simple.

Differential Revision: https://reviews.llvm.org/D88718

GitOrigin-RevId: f0785c1f7acd34ec6681f188afedc9be89ba0cc4
diff --git a/include/CMakeLists.txt b/include/CMakeLists.txt
index 1c3468e..e0f05da 100644
--- a/include/CMakeLists.txt
+++ b/include/CMakeLists.txt
@@ -154,6 +154,7 @@
   support/ibm/xlocale.h
   support/musl/xlocale.h
   support/newlib/xlocale.h
+  support/nuttx/xlocale.h
   support/solaris/floatingpoint.h
   support/solaris/wchar.h
   support/solaris/xlocale.h
diff --git a/include/__config b/include/__config
index 0006897..59aa922 100644
--- a/include/__config
+++ b/include/__config
@@ -1121,6 +1121,7 @@
 #  if defined(__FreeBSD__) || \
       defined(__wasi__) || \
       defined(__NetBSD__) || \
+      defined(__NuttX__) || \
       defined(__linux__) || \
       defined(__GNU__) || \
       defined(__APPLE__) || \
@@ -1223,7 +1224,7 @@
 #  endif
 #endif
 
-#if defined(__BIONIC__) || defined(__CloudABI__) || \
+#if defined(__BIONIC__) || defined(__CloudABI__) || defined(__NuttX__) ||      \
     defined(__Fuchsia__) || defined(__wasi__) || defined(_LIBCPP_HAS_MUSL_LIBC) || \
     defined(__MVS__)
 #define _LIBCPP_PROVIDES_DEFAULT_RUNE_TABLE
diff --git a/include/__locale b/include/__locale
index d4f3cda..fd09206 100644
--- a/include/__locale
+++ b/include/__locale
@@ -22,6 +22,8 @@
 #if defined(_LIBCPP_MSVCRT_LIKE)
 # include <cstring>
 # include <support/win32/locale_win32.h>
+#elif defined(__NuttX__)
+# include <support/nuttx/xlocale.h>
 #elif defined(_AIX) || defined(__MVS__)
 # include <support/ibm/xlocale.h>
 #elif defined(__ANDROID__)
diff --git a/include/support/nuttx/xlocale.h b/include/support/nuttx/xlocale.h
new file mode 100644
index 0000000..b70d620
--- /dev/null
+++ b/include/support/nuttx/xlocale.h
@@ -0,0 +1,18 @@
+// -*- C++ -*-
+//===-------------------- support/nuttx/xlocale.h -------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP_SUPPORT_NUTTX_XLOCALE_H
+#define _LIBCPP_SUPPORT_NUTTX_XLOCALE_H
+
+#if defined(__NuttX__)
+#include <support/xlocale/__posix_l_fallback.h>
+#include <support/xlocale/__strtonum_fallback.h>
+#endif // __NuttX__
+
+#endif
diff --git a/src/include/config_elast.h b/src/include/config_elast.h
index 501cbc4..3113f9f 100644
--- a/src/include/config_elast.h
+++ b/src/include/config_elast.h
@@ -17,10 +17,14 @@
 #include <errno.h>
 #endif
 
+// Note: _LIBCPP_ELAST needs to be defined only on platforms
+// where strerror/strerror_r can't handle out-of-range errno values.
 #if defined(ELAST)
 #define _LIBCPP_ELAST ELAST
 #elif defined(_NEWLIB_VERSION)
 #define _LIBCPP_ELAST __ELASTERROR
+#elif defined(__NuttX__)
+// No _LIBCPP_ELAST needed on NuttX
 #elif defined(__Fuchsia__)
 // No _LIBCPP_ELAST needed on Fuchsia
 #elif defined(__wasi__)
diff --git a/src/locale.cpp b/src/locale.cpp
index 5fdc149..ed93727 100644
--- a/src/locale.cpp
+++ b/src/locale.cpp
@@ -30,7 +30,7 @@
 #include "__sso_allocator"
 #if defined(_LIBCPP_MSVCRT) || defined(__MINGW32__)
 #include "support/win32/locale_win32.h"
-#elif !defined(__BIONIC__)
+#elif !defined(__BIONIC__) && !defined(__NuttX__)
 #include <langinfo.h>
 #endif
 #include <stdlib.h>