创建，添加sdram

rt-thread/components/libc/compilers/common/extension/SConscript

@@ -0,0 +1,21 @@
+import os
+from building import *
+Import('rtconfig')
+
+src   = []
+cwd   = GetCurrentDir()
+CPPPATH = [cwd]
+group = []
+
+src += Glob('*.c')
+
+if rtconfig.PLATFORM not in ['gcc', 'llvm-arm']:
+    group = DefineGroup('Compiler', src, depend = [''], CPPPATH = CPPPATH)
+
+list = os.listdir(cwd)
+for d in list:
+    path = os.path.join(cwd, d)
+    if os.path.isfile(os.path.join(path, 'SConscript')):
+        group = group + SConscript(os.path.join(d, 'SConscript'))
+
+Return('group')