archivers/arj: fix build with clang 18

Clang 18 no longer accepts -export-dynamic, which is a linker option,
resulting in an error building archivers/arj:

cc: error: unknown argument: '-export-dynamic'

Fix this by using the correct spelling, -Wl,--export-dynamic.

PR: 276747
Approved by: garga (maintainer)
MFH: 2024Q1