Seed unsafeGlobalDynFlags with enough information to use ppr

At the moment the pretty-printer isn't functional if used before DynFlags is initialized by initGhcMonad. In particular things like pprPanic aren't usable since unsafeGlobalDynFlags isn't yet initialized. This is quite annoying during development.

It seems like it should be possible to seed unsafeGlobalDynFlags with some minimal DynFlags, presumably with rather verbose output (as this is presumably what you want when debugging a compiler crash early in startup).

Trac metadata

Trac field	Value
Version	7.10.3
Type	Task
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture

changed weight to 5

added Ttask Trac import labels

Trac metadata

Trac field	Value
Differential revisions	- → D2036

mentioned in commit 4e98b4ff

mentioned in commit e8d35677

closed

changed milestone to %8.0.1

Merged to ghc-8.0 as well.

Trac metadata

Trac field	Value
TypeOfFailure	OtherFailure → CompileTimeCrash
Resolution	Unresolved → ResolvedFixed

added compiler crash label

added Pnormal label