Add macros to return pre-defined MPIs.
* src/gcrypt.h.in (GCRYMPI_CONST_ONE, GCRYMPI_CONST_TWO) (GCRYMPI_CONST_THREE, GCRYMPI_CONST_FOUR, GCRYMPI_CONST_EIGHT): New. (_gcry_mpi_get_const): New private function. * src/visibility.c (_gcry_mpi_get_const): New. * src/visibility.h: Mark it visible.
- Signed-off-by: Werner Koch <wk@gnupg.org>