While we previously checked the safety of safe imported modules we
didn't do this check transitively. This can be a problem when we depend
on a trustworthy module in a package that is no longer trusted, so we
should fail compilation. We already stored in an interface file the
transitive list of packages a module depends on. Now we extend that list
to include a flag saying if we depend on that package being trusted as
well.

Comment was removed as I thought it was incorrect now with code
changes but Simon M thinks my interpretation of the comment
was incorrect. He isn't sure what the comment is refereeing to
either though! So have restored comment and created trac #5249
to track fixing this at some point.

For instance decls we no longer store the SafeHaskell mode
in this data structure but instead store it as a bool field
in the overlap flag structure.

This was done as we originally planned for SafeHaskell to provide
some compilation safety. We have dropped this though and instead
intend for a new static flag, '--safecompile' that provides
this instead in an orthogonal way to SafeHaskell.

Now ghc supports:
  - trust => Set a package to be trusted
  - distrust => Set a package to be untrusted
  - distrust-all-package => Set all packages to be untrusted by default

OverlappingInstances in Safe modules can only overlap instances
defined in the same module.

Problem with -fforce-recomp not picking up changed Safe flags correctly
fixed. Also now disable Template Haskell completely.

This patch disables the use of some GHC extensions in
Safe mode and also the use of certain flags. Some
are disabled completely while others are only allowed
on the command line and not in source PRAGMAS.

We also check that Safe imports are indeed importing
a Safe or Trustworthy module.

Assigning the arguments to temporaries was only needed in the case of
emitCopyArray, where the arguments are alive across the call.  That is
not the case in emitCopyByteArray.
Signed-off-by: David Terei <davidterei@gmail.com>

I'm not sure what's going on with these warnings, but for now
I've suppressed them all.