pregen: Fix the parallel build problem in pregen target
pregen: Fix the parallel build problem in pregen target

* pregen-headers really need the headers to get themselves generated.
  so we create explicit dependency and invoke make as an action on
  pregen. This fixes the parallel build issue for better.

Signed-off-by: Khem Raj <729d64b6f67515e258459a5f6d20ec88b2caf8df@gmail.com>

joel-porquet/tsar-uclibc,joel-porquet/tsar-uclibc,joel-porquet/tsar-uclibc,joel-porquet/tsar-uclibc