创建，添加sdram

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

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+from building import *
+Import('rtconfig')
+
+src   = Glob('*.c')
+group = []
+
+if rtconfig.PLATFORM in ['armcc', 'armclang']:
+    CPPDEFINES = ['RT_USING_ARMLIBC', 'RT_USING_LIBC', '__STDC_LIMIT_MACROS']
+    AddDepend(['RT_USING_ARMLIBC', 'RT_USING_LIBC'])
+    group = DefineGroup('Compiler', src, depend = [''], CPPDEFINES = CPPDEFINES)
+
+Return('group')