build: Support specifying HMAC key by --enable-hmac-binary-check.
* configure.ac (DEF_HMAC_BINARY_CHECK): New SUBSTITUTION. (DL_LIBS): Fix the condition. * src/Makefile.am (libgcrypt_la_CFLAGS): Use DEF_HMAC_BINARY_CHECK. (hmac256_CFLAGS): Likewise.
- GnuPG-bug-id: T5550
- Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>