创建，添加sdram

rt-thread/components/libc/compilers/dlib/SConscript

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+from building import *
+Import('rtconfig')
+
+src   = Glob('*.c')
+group = []
+
+if rtconfig.PLATFORM in ['iccarm']:
+    CPPDEFINES = ['RT_USING_DLIBC', 'RT_USING_LIBC', '_DLIB_ADD_EXTRA_SYMBOLS=0']
+    AddDepend(['RT_USING_DLIBC', 'RT_USING_LIBC'])
+
+    if GetDepend('DFS_USING_POSIX'):
+        from distutils.version import LooseVersion
+        from iar import IARVersion
+
+        CPPDEFINES = CPPDEFINES + ['_DLIB_FILE_DESCRIPTOR']
+        iar_version = LooseVersion(IARVersion())
+        if iar_version != LooseVersion("0.0") and iar_version < LooseVersion("8.20.1"):
+            CPPDEFINES = CPPDEFINES + ['_DLIB_THREAD_SUPPORT']
+
+    group = DefineGroup('Compiler', src, depend = [''], CPPDEFINES = CPPDEFINES)
+
+Return('group')