move to external.

git-svn-id: https://rt-thread.googlecode.com/svn/trunk@1304 bbd45198-f89e-11dd-88c7-29a3b14d5316

components/external/libpng/SConscript

@@ -0,0 +1,28 @@
+Import('RTT_ROOT')
+Import('rtconfig')
+from building import *
+
+src	= Split('''
+png.c
+pngerror.c
+pnggccrd.c
+pngget.c
+pngmem.c
+pngpread.c
+pngread.c
+pngrio.c
+pngrtran.c
+pngrutil.c
+pngset.c
+pngtrans.c
+pngvcrd.c
+pngwio.c
+pngwrite.c
+pngwtran.c
+pngwutil.c
+''')
+CPPPATH = [RTT_ROOT + '/components/rtgui/common/libpng']
+
+group = DefineGroup('libpng', src, depend = ['RTGUI_IMAGE_PNG'], CPPPATH = CPPPATH)
+
+Return('group')