math/linpack: 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
(cherry picked from commit ab2d219b7da1424f320842297d03c73b5c12bf76)