Error in Compiling SDL during the tutorial of "Building Apps and Kernels" in the Wiki

follow the instruction of the tutorial, when making toolchain, some errors came out for SDL.

cc1: warning: include location "/usr/include" is unsafe for cross-compilation
cc1: warning: include location "/usr/include/directfb" is unsafe for cross-compilation
./src/audio/dma/SDL_dmaaudio.c: In function 'DMA_WaitAudio':
./src/audio/dma/SDL_dmaaudio.c:166: error: impossible constraint in 'asm'
make[2]: *** [build/SDL_dmaaudio.lo] Error 1
make[2]: Leaving directory `/srv/preware/build/toolchain/libsdl/build/src'
make[1]: *** [build/armv7.built-1.2-1] Error 2
make[1]: Leaving directory `/srv/preware/build/toolchain/libsdl'
make: *** [staging/usr/include/SDL/SDL.h] Error 2

the tutorial link here: [url=http://www.webos-internals.org/wiki/Building_Apps_and_Kernels]Building Apps and Kernels - WebOS Internals[/url]


it seems that the include is unsafe. So how can i do?