Packages/Rts: add `linker` to RTS directories
Packages/Rts: add `linker` to RTS directories

Recent commit split off the m32 allocator to `rts/linker/`, which
broke the build using Hadrian (since it didn't know about the new
directory). This fixes it.

Signed-off-by: Michal Terepeta <369df49275e5bc251c4c73f6250cec386e4069c3@gmail.com>

sdiehl/ghc,bgamari/shaking-up-ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,izgzhen/hadrian,snowleopard/hadrian,snowleopard/shaking-up-ghc,sdiehl/ghc