* cipher/Makefile.am (libcipher_la_SOURCES): Add kem-ecc.{c,h}.
* cipher/kem-ecc.c: New.
* cipher/kem-ecc.h: New.
* cipher/kem.c (_gcry_kem_keypair): Dispatch to _gcry_ecc_raw_keypair.
(_gcry_kem_encap): Dispatch to _gcry_ecc_raw_encap,
_gcry_ecc_dhkem_encap, _gcry_openpgp_kem_encap, and
_gcry_cms_kem_encap.
(_gcry_kem_decap): Dispatch to _gcry_ecc_raw_decap,
_gcry_ecc_dhkem_decap, _gcry_openpgp_kem_decap, and
_gcry_cms_kem_decap.
* src/gcrypt.h.in: Add constants for ECC KEM.
* tests/t-kem.c (test_kem_raw_x25519, test_kem_dhkem_x25519)
(test_kem_openpgp_x25519, test_kem_cms_x25519): New.
(check_kem, main): Add tests for ECC KEM.