Looking into the ./configure script, I noticed the script doesn't look into the environmental variable that I give. I just modified the script (Line 4067) to get it work.
if test "$PHP_GETTEXT" != "no"; then
for i in $PHP_GETTEXT /usr/local /usr /usr/local/opt/gettext; do
test -r $i/include/libintl.h && GETTEXT_DIR=$i && break
done