x86_64-nacl-gcc: not found

x86_64-nacl-gcc: not found

I downloaded the cocos2d-x-2.1.5 and configured the NDK_ROOT_LOCAL &
ANDROID_SDK_ROOT_LOCAL variables, and run the command export
NACL_SDK_ROOT=/my/path/to/NACL_SDK/pepper_28, when I run the script
build-nacl.sh, it reports the error x86_64-nacl-gcc: not found as blow:
codingchan@CC-mbp:/data/build/cocos2d-x-2.1.5$ ./build-nacl.sh
+ cd .
+ mkdir -p lib/nacl/Debug/
+ mkdir -p lib/nacl/Release/
+ export 'MAKEFLAGS=-j10 PLATFORM=nacl'
+ MAKEFLAGS='-j10 PLATFORM=nacl'
+ '[' '' = clean ']'
+ make DEBUG=1 all make -C external/chipmunk/proj.nacl all make[1]:
Entering directory
`/data/build/cocos2d-x-2.1.5/external/chipmunk/proj.nacl' CC
obj/x86_64/Debug/src/chipmunk.o /bin/sh: 1: x86_64-nacl-gcc: not found CC
obj/x86_64/Debug/src/cpBody.o /bin/sh: 1: x86_64-nacl-gcc: not found CC
obj/x86_64/Debug/src/cpSpace.o /bin/sh: 1: make[1]: ***
[obj/x86_64/Debug/src/chipmunk.o] Error 127 make[1]: *** Waiting for
unfinished jobs.... make[1]: *** [obj/x86_64/Debug/src/cpBody.o] Error 127
x86_64-nacl-gcc: not found make[1]: *** [obj/x86_64/Debug/src/cpSpace.o]
Error 127 make[1]: Leaving directory
`/data/build/cocos2d-x-2.1.5/external/chipmunk/proj.nacl' make: *** [all]
Error 2
according to this post, I checked my ia32-libs, it's already installed, my
system is Ubuntu 13.04 x86_64, could anyone help? Thx a lot.