GHC 8.0.2: use -split-sections

-split-sections replaced -split-objs with following upsides:

1) -split-objs adds considerable overhead to compile time

2) combined with stripping, it causes issues when cross-compiling

For upstream see https://ghc.haskell.org/trac/ghc/ticket/8405

This is supported only for Linux/Windows using ld linker.

GHC master also turns on -split-sections by default.

Example using stack:

Without splitting

  $ du /nix/store/5paayhibayr73zqfaj458g4k4mv108jn-stack-1.3.2
  4       /nix/store/5paayhibayr73zqfaj458g4k4mv108jn-stack-1.3.2/share/bash-completion/completions
  4       /nix/store/5paayhibayr73zqfaj458g4k4mv108jn-stack-1.3.2/share/bash-completion
  4       /nix/store/5paayhibayr73zqfaj458g4k4mv108jn-stack-1.3.2/share
  23416   /nix/store/5paayhibayr73zqfaj458g4k4mv108jn-stack-1.3.2/bin
  23420   /nix/store/5paayhibayr73zqfaj458g4k4mv108jn-stack-1.3.2

With -split-objs

  $ du /nix/store/fypymm529adpx71gdzm0851xz42wdbz0-stack-1.3.2
  20632   /nix/store/fypymm529adpx71gdzm0851xz42wdbz0-stack-1.3.2/bin
  4 /nix/store/fypymm529adpx71gdzm0851xz42wdbz0-stack-1.3.2/share/bash-completion/completions
  4 /nix/store/fypymm529adpx71gdzm0851xz42wdbz0-stack-1.3.2/share/bash-completion
  4       /nix/store/fypymm529adpx71gdzm0851xz42wdbz0-stack-1.3.2/share
  20636   /nix/store/fypymm529adpx71gdzm0851xz42wdbz0-stack-1.3.2

With -split-sections

  $ du /nix/store/40l6krinx1zx41lr87c4m12hxj4ldf3x-stack-1.3.2
  4       /nix/store/40l6krinx1zx41lr87c4m12hxj4ldf3x-stack-1.3.2/share/bash-completion/completions
  4       /nix/store/40l6krinx1zx41lr87c4m12hxj4ldf3x-stack-1.3.2/share/bash-completion
  4       /nix/store/40l6krinx1zx41lr87c4m12hxj4ldf3x-stack-1.3.2/share
  20672   /nix/store/40l6krinx1zx41lr87c4m12hxj4ldf3x-stack-1.3.2/bin
  20676   /nix/store/40l6krinx1zx41lr87c4m12hxj4ldf3x-stack-1.3.2

Note: you currently need following overrides to build stack on 802:

   vector-algorithms = dontCheck super.vector-algorithms;
   path-io = doJailbreak super.path-io;
   stack = doJailbreak super.stack;

Note: Should also work on GHC 8.0.1, but I'm being careful here.
      We could backport later on.