Pass build/host/target through to libffi as well

Fixes the issue on Raspberry Pi with a 64-bit kernel with a 32-bit
userland. (I hope)

3rdp/build/js-libffi-prefix.patch

@@ -5,7 +5,7 @@
  if test "$JS_HAS_CTYPES"; then
    # Run the libffi 'configure' script.
 -  ac_configure_args="--disable-shared --enable-static --disable-raw-api"
-+  ac_configure_args="--disable-shared --enable-static --disable-raw-api --prefix=${prefix}"
++  ac_configure_args="--disable-shared --enable-static --disable-raw-api --prefix=${prefix} --build=${build} --host=${host} --target=${target}"
    if test "$MOZ_DEBUG"; then
      ac_configure_args="$ac_configure_args --enable-debug"
    fi
@@ -16,7 +16,7 @@
  if test "$JS_HAS_CTYPES"; then
    # Run the libffi 'configure' script.
 -  ac_configure_args="--disable-shared --enable-static --disable-raw-api"
-+  ac_configure_args="--disable-shared --enable-static --disable-raw-api --prefix=${prefix}"
++  ac_configure_args="--disable-shared --enable-static --disable-raw-api --prefix=${prefix} --build=${build} --host=${host} --target=${target}"
    if test "$MOZ_DEBUG"; then
      ac_configure_args="$ac_configure_args --enable-debug"
    fi