[LIBC] Use RT_USING_LIBC instead of libs option for each compiler

[BernardXiong]

No description provided.

[aozima]

这样挺好！

[grissiom]

There are still many RT_USING_NEWLIB in the source code:

% git grep RT_USING_NEWLIB src/ components/
components/dfs/filesystems/nfs/rpc/types.h:#ifndef RT_USING_NEWLIB
components/dfs/filesystems/nfs/rpc/types.h:#if !defined(RT_USING_NEWLIB) && !defined(RT_USING_MINILIBC)
components/dfs/filesystems/yaffs2/yaffs.diff:+  #ifdef RT_USING_NEWLIB
components/dfs/include/dfs_def.h:#if defined(RT_USING_NEWLIB) 
components/dfs/include/dfs_posix.h:#ifndef RT_USING_NEWLIB
components/external/SQLite-3.8.1/SQLiteLib/sqlite3.c:#ifndef RT_USING_NEWLIB
components/external/SQLite-3.8.1/SQLiteLib/sqlite3.c:#endif /* RT_USING_NEWLIB */
components/external/SQLite-3.8.1/src/os_rtthread.c:#ifndef RT_USING_NEWLIB
components/external/SQLite-3.8.1/src/os_rtthread.c:#endif /* RT_USING_NEWLIB */
components/external/cairo/SConscript:group = DefineGroup('cairo', src, depend = ['RT_USING_CAIRO', 'RT_USING_NEWLIB', 'RTGUI_IMAGE_PNG', 'RT_USING_PTHREADS'], CPPPATH = CPPPATH)
components/external/espruino/SConscript:group = DefineGroup('Espruino', src, depend = ['RT_USING_JS', 'RT_USING_NEWLIB'], CPPPATH = path)
components/external/libpng/pngconf.h:#ifndef RT_USING_NEWLIB
components/external/lua/README.TXT:    - 采用gcc工具链时，依赖于newlib，需在rtconfig.h中定义RT_USING_NEWLIB
components/finsh/finsh.h:#if defined(RT_USING_NEWLIB) || defined (RT_USING_MINILIBC)
components/init/components.c:#ifdef RT_USING_NEWLIB
components/init/components.h:#ifdef RT_USING_NEWLIB
components/libc/minilibc/ctype.c:#if !defined (RT_USING_NEWLIB) && defined (RT_USING_MINILIBC)
components/libc/minilibc/stdlib.c:#if !defined (RT_USING_NEWLIB) && defined (RT_USING_MINILIBC)
components/libc/minilibc/stdlib.h:#if !defined (RT_USING_NEWLIB) && defined (RT_USING_MINILIBC)
components/libc/minilibc/string.c:#if !defined (RT_USING_NEWLIB) && defined (RT_USING_MINILIBC)
components/libc/minilibc/string.h:#if !defined (RT_USING_NEWLIB) && defined (RT_USING_MINILIBC)
components/libc/newlib/SConscript:CPPDEFINES = ['RT_USING_NEWLIB']
components/net/lwip-1.3.2/src/arch/include/arch/cc.h:#ifdef RT_USING_NEWLIB
components/net/lwip-1.3.2/src/lwipopts.h:#ifdef RT_USING_NEWLIB
components/net/lwip-1.4.1/src/arch/include/arch/cc.h:#ifdef RT_USING_NEWLIB
components/net/lwip-head/src/arch/include/arch/cc.h:#ifdef RT_USING_NEWLIB
components/net/lwip/src/arch/include/arch/cc.h:#ifdef RT_USING_NEWLIB
components/pthreads/posix_types.h:#ifdef RT_USING_NEWLIB
src/kservice.c:#if !defined (RT_USING_NEWLIB) && defined (RT_USING_MINILIBC) && defined (__GNUC__)

[BernardXiong]

When using RT_USING_LIBC, if the GCC is used, the RT_USING_NEWLIB will be appended by SConscript file to make a compatible with old setting.

[grissiom]

Oh, I see...