build-python: Build the native libffi as a static library only

This fixes importing the _ctypes module, if a shared libffi doesn't
happen to exist on the host system with the right so version.
Since Python 3.12, such a build error ends up failing the build,
while it previously passed silently even if some parts of the build
had failed.

build-python.sh

@@ -92,7 +92,7 @@ if [ -z "$HOST" ]; then
     [ -z "$CLEAN" ] || rm -rf $BUILDDIR
     mkdir -p $BUILDDIR
     cd $BUILDDIR
-    ../configure --prefix="$PREFIX" --disable-symvers --disable-docs
+    ../configure --prefix="$PREFIX" --disable-symvers --disable-docs --disable-shared
     $MAKE -j$CORES
     $MAKE install
     cd ../..