databases/p5-DBD-Oracle: fix build using lld

While using LLVM's lld linker as /usr/bin/ld the build breaks
because Oracle supplied libs built without -fPIC:

can't create dynamic relocation R_386_32 ... in readonly segment

It is not possible to recompile Oracle object files with -fPIC,
so fix this overriding lld's default and make it the same as GNU ld
allowing .text relocations.

This fixes build error, so no PORTREVISION bump.

Reported by: emaste