export INSTALLPREFIX=/path/to/install
export SDK=/Developer/SDKs/MacOSX10.5.sdk
export MACOSX_DEPLOYMENT_TARGET=10.5

./Configure -ders \
-Dcc=gcc-4.0 \
-Dld=g++-4.0 \
-Dusethreads \
-Duseithreads \
-Ud_sigsetjmp \
-Uinstallusrbinperl \
-Ulocincpth= \
-Uloclibpth= \
-Ud_poll \
-Ui_poll \
-Ud_sockatmark \
-Ud_sockatmarkproto \
-Ui_libutil \
-Aldflags="-Wl,-search_paths_first" \
-Alddlflags="-Wl,-search_paths_first" \
-Accflags="-arch i386" \
-Aldflags="-arch i386" \
-Alddlflags="-arch i386" \
-Accflags="-nostdinc -B$SDK/usr/include/gcc -B$SDK/usr/lib/gcc -isystem$SDK/usr/include -F$SDK/System/Library/Frameworks -mmacosx-version-min=10.5" \
-Aldflags="-Wl,-syslibroot,$SDK -mmacosx-version-min=10.5" \
-Alddlflags="-Wl,-syslibroot,$SDK -mmacosx-version-min=10.5" \
-Accflags="-DUSE_SITECUSTOMIZE -Duselargefiles" \
-Accflags="-fno-merge-constants" \
-Dprefix=$INSTALLPREFIX \
-Dsed=/usr/bin/sed \
-Duseshrplib