Unused variable warnings

[selsta]

/Users/selsta/dev/monero/external/supercop/crypto_sign/ed25519/amd64-64-24k/ge25519_scalarmult_base.c:15:22: warning: unused variable 'ecd' [-Wunused-const-variable]
static const fe25519 ecd = {{0x75EB4DCA135978A3, 0x00700A4D4141D8AB, 0x8CC740797779E898, 0x52036CEE2B6FFE73}};
                     ^
1 warning generated.

I have been fixing warnings for the monero repo and these show up on Mac clang for supercop.

[vtnerd]

I'll see if cmake can suppress these specific files. I'd prefer not changing them because these lines are unaltered from upstream supercop currently.