component/libffi: add support for riscv architecture

by default on riscv architecture, the libffi.so will be placed in
lib/lp64d but everywhere else in buildout (and especially for the
compilation of python3) we expect the lib to be in lib/ directory.

component/libffi/buildout.cfg

@@ -16,6 +16,7 @@ patch-options = -p1
 patches =
   ${:_profile_base_location_}/libdir.patch#f7274250c8ca43b10e7fc968f730b833
 configure-options =
+  --disable-multi-os-directory
   --disable-static
   --enable-portable-binary
   --with-gcc-arch=generic