security/xmlsec1: unbreak on 9.x

signatures.c:36: error: expected declaration specifiers or '...' before 'ECDSA_SIG'
signatures.c: In function 'ECDSA_SIG_get0':
signatures.c:38: error: 'sig' undeclared (first use in this function)
signatures.c:38: error: (Each undeclared identifier is reported only once
signatures.c:38: error: for each function it appears in.)

Reported by: pkg-fallout
Approved by: portmgr blanket