[nano] rt-thread susport nano option

components/libc/Kconfig

@@ -1,20 +1,6 @@
 menu "C/C++ and POSIX layer"
 
-config RT_USING_INTERNAL_LIBC_ONLY
-    bool "Only use tool chain internal libc"
-    default n
-    help
-        This option is for RT-Thread Nano version.
-        If select this option, it will not compile components/libc
-        folder and only use tool chain internal libc. Normally, the
-        tool chain internal is only cover ISO standard (e.g. armcc),
-        but some tool chains' internal libc will cover more than
-        ISO standard (e.g. newlib). However, no matter the cover level
-        it is, the rt-thread libc leveling layer will not be involved
-        at all if select this option.
-
 config RT_USING_EXTERNAL_LIBC
-    depends on !RT_USING_INTERNAL_LIBC_ONLY
     bool
     help
         This is for external libc(e.g. mlib),

components/libc/SConscript

@@ -7,9 +7,10 @@ cwd = GetCurrentDir()
 objs = []
 list = os.listdir(cwd)
 
-for d in list:
-    path = os.path.join(cwd, d)
-    if os.path.isfile(os.path.join(path, 'SConscript')):
-        objs = objs + SConscript(os.path.join(d, 'SConscript'))
+if not GetDepend('RT_USING_NANO'):
+    for d in list:
+        path = os.path.join(cwd, d)
+        if os.path.isfile(os.path.join(path, 'SConscript')):
+            objs = objs + SConscript(os.path.join(d, 'SConscript'))
 
 Return('objs')

components/libc/compilers/SConscript

@@ -7,10 +7,9 @@ cwd = GetCurrentDir()
 objs = []
 list = os.listdir(cwd)
 
-if not GetDepend('RT_USING_INTERNAL_LIBC_ONLY'):
-    for d in list:
-        path = os.path.join(cwd, d)
-        if os.path.isfile(os.path.join(path, 'SConscript')):
-            objs = objs + SConscript(os.path.join(d, 'SConscript'))
+for d in list:
+    path = os.path.join(cwd, d)
+    if os.path.isfile(os.path.join(path, 'SConscript')):
+        objs = objs + SConscript(os.path.join(d, 'SConscript'))
 
 Return('objs')