databases/mongodb34: add support for aarch64

Commit important part of PR missed in previous commit.

PR: 229602
Submitted by: Ronald Klop <ronald-lists@klop.ws>
Reported by: Ronald Klop <ronald-lists@klop.ws>
Approved by: eric@camachat.org (maintainer timeout, > 2 weeks)
Pointyhat to: swills