ghc: allow --show-options and --interactive together

Summary:
Previously 'ghc --show-options' showed all options that GHC can possibly
accept. With this patch, it'll only show the options that have effect in
non-interactive modes.
This change also adds support for using 'ghc --interactive --show-options'
which previously was disallowed. This command will show all options that have
effect in the interactive mode.
The CmdLineParser is updated to know about the GHC modes, and then each flag
is annotated with which mode it has effect.
This fixes #9259.

Test Plan:
Try out --show-options with --interactive on the command line. With and without
--interactive should give different results.
Run the test suite, mode001 has been updated to verify this new flag
combination.

Reviewers: austin, jstolarek

Reviewed By: austin, jstolarek

Subscribers: jstolarek, thomie, carter, simonmar

Differential Revision: https://phabricator.haskell.org/D337

GHC Trac Issues: #9259
Add -fdefer-typed-holes flag which defers hole errors to runtime.

Summary:
As proposed by Richard on Trac. This patch adds a new flag -fdefer-typed-holes
and changes the semantics of the -fno-warn-typed-holes flag.

To summarise, by default GHC has typed holes enabled and produces a compile
error when it encounters a typed hole.

When -fdefer-type-errors OR -fdefer-typed-holes is enabled, hole errors are
converted to warnings and result in runtime errors when evaluated.

The warning flag -fwarn-typed-holes is on by default. Without -fdefer-type-errors
or -fdefer-typed-holes this flag is a no-op, since typed holes are an error
under these conditions. If either of the defer flags are enabled (converting
typed hole errors into warnings) the -fno-warn-typed-holes flag disables the
warnings. This means compilation silently succeeds and evaluating a hole will
produce a runtime error.

The rationale behind allowing typed holes warnings to be silenced is that tools
like Syntastic for vim highlight warnings and hole warnings may be undesirable.

Signed-off-by: Merijn Verstraaten <merijn@inconsistent.nl>

Test Plan: validate

Reviewers: austin, simonpj, thomie

Reviewed By: simonpj, thomie

Subscribers: Fuuzetsu, thomie, carter

Differential Revision: https://phabricator.haskell.org/D442

GHC Trac Issues: #9497

Conflicts:
	compiler/main/DynFlags.hs