[root@ffmpeg gpac]# gcc -o tmp.o tmp.c -lz -I/usr/local/myapps/include
/usr/bin/ld: cannot find -lz
collect2: ld returned 1 exit status

cat > $TMPC << EOF
#include <zlib.h>
int main( void ) { if (zlibVersion() != ZLIB_VERSION) { puts("zlib version differs !!!"); return 1; } return 0; }
EOF
has_zlib="no"
if $cc -o $TMPO $TMPC -lz 2> /dev/null ; then
has_zlib="system"
elif $cc -o $TMPO $TMPC -I$local_inc/zlib -L$local_lib -lz -I/usr/local/myapps/include -L/usr/local/myapps/lib 2> /dev/null  ; then
#elif $cc -o $TMPO $TMPC -I$local_inc/zlib -L$local_lib -lz  2> /dev/null  ; then
has_zlib="local"
else
  echo "error: zlib not found on system or in local libs"
  exit 1
fi

** Detected libraries **
zlib: local
OSS Audio: yes
ALSA Audio: no

positor/texturing.opic compositor/texturing_gl.opic compositor/visual_manager.opic compositor/visual_manager_2d.opic 
compositor/visual_manager_2d_draw.opic compositor/visual_manager_3d.opic compositor/visual_manager_3d_gl.opic
compositor/x3d_geometry.opic laser/lsr_enc.opic laser/lsr_dec.opic laser/lsr_tables.opic -lm
 -L/usr/local/lib -lGL -lglut -L../extra_lib/lib/gcc  -lz -lpthread -ldl
/usr/bin/ld: cannot find -lz
collect2: ld returned 1 exit status
make[1]: *** [libgpac.so] Error 1
make[1]: Leaving directory `/usr/src/gpac/src'
make: *** [lib] Error 2

make --environment-overrides -I/usr/local/myapps/include
make  --environment-overrides -I/usr/local/myapps/include install

[root@ffmpeg gpac]# /usr/local/myapps/bin/MP4Box -version
MP4Box - GPAC version 0.4.5 (build 33)
GPAC Copyright: (c) Jean Le Feuvre 2000-2005
                (c) ENST 2005-200X