Rip out ld.bfd-specific link options from driver

For as long as I can remember GHC has been hard-coded to add --reduce-memory-overheads and --hash-size=-31 to the linker command-line when it thinks it's using ld.bfd (see GHC.SysTools.Info). It appears that this logic was introduced due to #5240 (closed), which appears to be concerned with the old -split-objs method of dead-code dropping. Not only is it quite unclear whether this logic is necessary or helpful with -split-sections, it's very likely that it is significantly blowing up link times.

While the documentation claims that the --reduce-memory-overheads may reduce memory consumption by anywhere from 0% to 40%, @Phyx suggests that the high end is likely an outlier. Moreover, he points out that the flag changes the link map generation from a linear to a quadratic algorithm.

We should remove this logic and, if it's still helpful, move it into the configure script where it belongs.