libcxx: optional wide characters support.

Disable wchar can reduce approximately 1/3 of the libcxx.
mainly from locale, string and streams.

Platform: sim
Figures: bin size in bytes.

   Size   | Description
----------+------------------------------------------------
 10045336 | Base, enable libcxx whithout any cxx programs.
 42067224 | Add cxxtest.
 29997304 | Disable libcxx wchar support.

Signed-off-by: jihandong <jihandong@xiaomi.com>

libs/libxx/Kconfig

@@ -112,11 +112,10 @@ config CXX_EXCEPTION
 config CXX_RTTI
 	bool "Enable RTTI Support"
 
-if UCLIBCXX
+config CXX_WCHAR
+	bool "Enable Wide Character Support"
 
-config UCLIBCXX_WCHAR
+if UCLIBCXX
-	bool "Enable Wide Stream Support"
-	default n
 
 config UCLIBCXX_BUFSIZE
 	int "IO Stream/Container Buffer Size"

libs/libxx/__config_site

@@ -9,6 +9,8 @@
 #ifndef _LIBCPP___CONFIG_SITE
 #define _LIBCPP___CONFIG_SITE
 
+#include <nuttx/config.h>
+
 #define _LIBCPP_ABI_VERSION 1
 #define _LIBCPP_ABI_NAMESPACE __1
 /* #undef _LIBCPP_ABI_FORCE_ITANIUM */
@@ -26,7 +28,9 @@
 /* #undef _LIBCPP_HAS_NO_FILESYSTEM */
 /* #undef _LIBCPP_HAS_NO_RANDOM_DEVICE */
 /* #undef _LIBCPP_HAS_NO_LOCALIZATION */
-/* #undef _LIBCPP_HAS_NO_WIDE_CHARACTERS */
+#ifndef CONFIG_CXX_WCHAR
+#define _LIBCPP_HAS_NO_WIDE_CHARACTERS
+#endif
 #define _LIBCPP_ENABLE_ASSERTIONS_DEFAULT 0
 
 // PSTL backends

libs/libxx/system_configuration.h

@@ -55,7 +55,7 @@
 
 /* String and I/O Stream Support */
 
-#ifdef CONFIG_UCLIBCXX_WCHAR
+#ifdef CONFIG_CXX_WCHAR
 #  define __UCLIBCXX_HAS_WCHAR__ 1
 #endif
 #define __UCLIBCXX_IOSTREAM_BUFSIZE__ CONFIG_UCLIBCXX_BUFSIZE
@@ -65,7 +65,7 @@
 #define __UCLIBCXX_SUPPORT_COUT__ 1
 #define __UCLIBCXX_SUPPORT_CERR__ 1
 #define __UCLIBCXX_SUPPORT_CLOG__ 1
-#ifdef CONFIG_UCLIBCXX_WCHAR
+#ifdef CONFIG_CXX_WCHAR
 #  define __UCLIBCXX_SUPPORT_WCIN__ 1
 #  define __UCLIBCXX_SUPPORT_WCOUT__ 1
 #  define __UCLIBCXX_SUPPORT_WCERR__ 1