Then, I tried to reinstall luaexpat:
ser:/usr/src/luaexpat-1.1# make clean
rm -f src/lxp.so.1.1.0 src/lxplib.o ../compat-5.1r5/compat-5.1.o
ser:/usr/src/luaexpat-1.1# make
gcc -Wall -pedantic -Waggregate-return -Wcast-align -Wmissing-prototypes
-Wstrict-prototypes -Wnested-externs -Wpointer-arith -Wshadow
-Wwrite-strings -ansi -O2 -I/usr/local/include -I../compat-5.1r5
-I/usr/local/include -c -o src/lxplib.o src/lxplib.c
gcc -c -Wall -pedantic -Waggregate-return -Wcast-align -Wmissing-prototypes
-Wstrict-prototypes -Wnested-externs -Wpointer-arith -Wshadow
-Wwrite-strings -ansi -O2 -I/usr/local/include -I../compat-5.1r5
-I/usr/local/include -o ../compat-5.1r5/compat-5.1.o
../compat-5.1r5/compat-5.1.c
export MACOSX_DEPLOYMENT_TARGET="10.3"; gcc -o src/lxp.so.1.1.0 -shared
src/lxplib.o ../compat-5.1r5/compat-5.1.o -lexpat
ser:/usr/src/luaexpat-1.1#
But after that, I still can't find the lxp.so file nor the lxp.lua file.