math/levmar: fix build on armv7

GNU ld supports neither -z relro nor -z norelro on armv7.
Unfortunately <bsd.lib.mk> insists on adding either to the link.
Work around this issue by using base ld for the link.

MFH: 2025Q2
Approved by: portmgr (build fix blanket)

(cherry picked from commit 3cc875416c55b3a5eb02cbfa3a2a29e5c665c87d)