Change all hashbangs to /usr/bin/env (#9057)

Summary:
```
git grep -l '#!' | xargs sed -i 's|#!.*/bin/\([^ ]*\)$|#!/usr/bin/env \1|'
```
and some manual tweaking

Test Plan: harbormaster

Reviewers: austin

Subscribers: hvr, simonmar, ezyang, carter

Differential Revision: https://phabricator.haskell.org/D237

GHC Trac Issues: #9057

compiler/count_bytes

-#! /usr/local/bin/perl
+#!/usr/bin/env perl
 #
 %DirCount = ();
 %ModCount = ();

distrib/cross-port

-#! /bin/bash
+#!/usr/bin/env bash
 
 # This script can be used to generate some unregisterised .hc files
 # for bootstrapping GHC on a new/unsupported platform.  It involves a

testsuite/tests/rename/prog006/Setup.lhs

-#!/usr/bin/runhaskell
+#!/usr/bin/env runhaskell
 > module Main where
 > import Distribution.Simple
 > main :: IO ()

utils/count_lines/count_lines.lprl

-#! /usr/bin/perl
+#!/usr/bin/env perl
 
 \begin{code}
 

utils/runghc/runghc.hs

@@ -7,7 +7,7 @@
 -- runghc program, for invoking from a #! line in a script.  For example:
 --
 --   script.lhs:
---      #!/usr/bin/env /usr/bin/runghc
+--      #!/usr/bin/env runghc
 --      > main = putStrLn "hello!"
 --
 -- runghc accepts one flag: