security/libgcrypt: update to 1.7.8

• Update libgcrypt to 1.7.8
• Bump library version in pkg-plist

Noteworthy changes in version 1.7.8

• Bug fixes:
  • Mitigate a flush+reload side-channel attack on RSA secret keys dubbed "Sliding right into disaster". For details see https://eprint.iacr.org/2017/627. [CVE-2017-7526]

Changes: https://lists.gnupg.org/pipermail/gnupg-announce/2017q2/000408.html
Binary compatibility report: https://abi-laboratory.pro/tracker/compat_report/libgcrypt/1.7.7/1.7.8/95cc7/abi_compat_report.html

PR: 220382
MFH: 2017Q3
Exp-run by: antoine
Security: https://www.vuxml.org/freebsd/ed3bf433-5d92-11e7-aa14-e8e0b747a45a.html