Pass some things to the linker that gcc passes. -r is the only one of these...

Pass some things to the linker that gcc passes.  -r is the only one of these that I'm sure about, but the others seem to be listed on FreeBSD by gcc -dumpspecs, so I hope they're right.  Apparently -r is also not passed on GNU/Linux (and should be), but I can't see where the toolchain definition for this platform live.

llvm-svn: 111114