Add basic support for locales in order to C++ streams to build and work for simple cases (POSIX / C locale).

Fix build with C++ GCC toolchain

libs/libc/locale/CMakeLists.txt

@@ -19,6 +19,13 @@
 # ##############################################################################
 
 if(CONFIG_LIBC_LOCALE)
-  target_sources(c PRIVATE lib_duplocale.c lib_freelocale.c lib_localeconv.c
-                           lib_newlocale.c lib_setlocale.c lib_uselocale.c)
+  target_sources(
+    c
+    PRIVATE lib_duplocale.c
+            lib_freelocale.c
+            lib_localeconv.c
+            lib_newlocale.c
+            lib_setlocale.c
+            lib_uselocale.c
+            lib_maxlocale.c)
 endif()

libs/libc/locale/Make.defs

@@ -25,6 +25,7 @@ ifeq ($(CONFIG_LIBC_LOCALE),y)
 CSRCS += lib_duplocale.c lib_freelocale.c lib_localeconv.c
 CSRCS += lib_newlocale.c lib_setlocale.c lib_uselocale.c
 CSRCS += lib_catalog.c lib_gettext.c lib_langinfo.c lib_iconv.c
+CSRCS += lib_maxlocale.c
 
 # Add the locale directory to the build
 

libs/libc/locale/lib_maxlocale.c

@@ -0,0 +1,45 @@
+/****************************************************************************
+ * libs/libc/locale/lib_maxlocale.c
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.  The
+ * ASF licenses this file to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance with the
+ * License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ *
+ ****************************************************************************/
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <nuttx/config.h>
+
+#include <stdlib.h>
+
+#ifdef CONFIG_LIBC_LOCALE
+
+/****************************************************************************
+ * Private Functions
+ ****************************************************************************/
+
+/* GNU libstdc++ is expecting some functions to be defined.
+ */
+
+/* Shall return the max number of bytes of a multibyte character */
+
+int __locale_mb_cur_max(void)
+{
+  return MB_CUR_MAX;
+}
+
+#endif