It seems there is a bug in RTS somewhere which makes libHSrts_thr_debug in a way it's including some symbols from the bfd library. The bug shows itself as a lot of testsuite tests failing with undefined symbols which originates in the BFD library. Example:

=====> cg013(threaded1)
cd ./codeGen/should_run && '/buildbot/ghc/kgardas/build/compiler/stage2/ghc-inplace' -no-recomp -dcore-lint -dcmm-lint -Di386_unknown_solaris2  -o cg013 cg013.hs -threaded -debug   >cg013.comp.stderr 2>&1
Compile failed (status 256) errors were:
Undefined                       first referenced
 symbol                             in file
bfd_openr                           /buildbot/ghc/kgardas/build/rts/libHSrts_thr_debug.a(Printer.thr_debug_o)
bfd_init                            /buildbot/ghc/kgardas/build/rts/libHSrts_thr_debug.a(Printer.thr_debug_o)
bfd_check_format_matches            /buildbot/ghc/kgardas/build/rts/libHSrts_thr_debug.a(Printer.thr_debug_o)
ld: fatal: Symbol referencing errors. No output written to cg013
collect2: ld returned 1 exit status