* cipher/Makefile.am (libcipher_la_SOURCES): Add kem.c.
* cipher/kem.c: New.
* src/gcrypt-int.h (_gcry_kem_keypair, _gcry_kem_encap)
(_gcry_kem_decap): New.
* src/gcrypt.h.in (gcry_kem_keypair, gcry_kem_encap)
(gcry_kem_decap): New.  Add constants.
* src/libgcrypt.def (gcry_kem_keypair, gcry_kem_encap)
(gcry_kem_decap): Add symbols.
* src/libgcrypt.vers: Likewise.