Remove uses of unsafeGlobalDynFlags for -fopt-coercions

Currently the -fopt-coercions flag finds its way to OptCoercion.optCoercion by way of the terrible unsafeGlobalDynFlags. In general it's nice to minimize the uses of unsafeGlobalDynFlags. However, it's not entirely clear that passing a DynFlags to optCoercion is worthwhile in this case as -fopt-coercion is essentially a debug flag. Leaving this here for later consideration.

Trac metadata

Trac field	Value
Version	8.2.1
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

closed

changed milestone to %8.6.1

This was fixed with 64c71ce9.

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedFixed
Differential revisions	- → D4774

added Pnormal label