build system woes in master

Currently it seems that master's build system has a few sticky points,

 * build.mk.sample adds dyn to GhcLibWays twice in the perf and
   perf-llvm flavors (added once in the global DYNAMIC_BY_DEFAULT check
   and again in the per-flavor PlatformSupportsSharedLibs). This leads
   to a multitude of make warnings complaining of multiply defined
   commands.

 * p_dyn is not built when p is. This causes build errors
   binaries regardless of whether profiling is enabled, this causes
   build errors when trying to build profiled binaries with the
   toolchain.

 * The p_dyn way appears to be broken with SplitObjs=YES, failing in the
   final phase of the build with errors of the form,

       /usr/bin/find: `libraries/ghc-prim/dist-install/build/GHC/Classes_p_dyn_o_split': No such file or directory
       /usr/bin/find: `libraries/ghc-prim/dist-install/build/GHC/CString_p_dyn_o_split': No such file or directory 

   Indeed, libraries/ghc-prim/dist-install/build/GHC/Classes_p_o_split
   exists but Classes_p_dyn_o_split does not.

Any thoughts about what might be going on with any of the above?

Cheers,

- Ben