BEGIN /tmp/ffmpeg-conf-29609-24537-2.c
    1
    2   #include <faad.h>
    3   int main(){
    4       (void) faacDecOpen;
    5       return 0;
    6   }
END /tmp/ffmpeg-conf-29609-24537-2.c
gcc -fomit-frame-pointer -c -o /tmp/ffmpeg-conf-4691-24537-27171.o /tmp/ffmpeg-conf-29609-24537-2.c
/tmp/ffmpeg-conf-29609-24537-2.c: In function `main':
/tmp/ffmpeg-conf-29609-24537-2.c:4: error: `faacDecOpen' not declared here 
ERROR: libfaad not found


But, 

grep faacDecOpen /usr/local/faad/include -r
/usr/local/faad/include/neaacdec.h:#define faacDecOpen                    NeAACDecOpen

and

grep neaacdec.h /usr/local/faad/include/ -r
/usr/local/faad/include/neaacdec.h:** $Id: neaacdec.h,v 1.11 2007/11/01 12:33:29 menno Exp $
/usr/local/faad/include/faad.h:#include "neaacdec.h"

How do I tell ffmpeg where is the install of faad I want to use?