Implement same specification as GHC spec file for mingw32

When the GCC driver envokes the pipeline a SPEC is used to determine how to configure the compiler and which libraries to pass along.

For Windows/mingw, this specfile is https://github.com/gcc-mirror/gcc/blob/master/gcc/config/i386/mingw32.h

This has a lot of interesting things that we need to emulate in order to be able to link as many things out of the box as GCC. In particular this is why you never need to specify -lgcc_s when compiling, but you do when using GHCi.

Or specifying what -mwindows links in, that when -lstdc++ is used what else to link in. Which base DLLs GCC will always link with when building an exe.

And how to link libgcc, either static or dynamically.

Currently we only support static linking of libgcc (which maybe we should change? or at least make user changeable).

The current partial implementation works by adding hooks into the RTS. A better implementation is adding it all outside the RTS in the DriverPipeline tied directly to the commandline options.

Trac metadata

Trac field	Value
Version	8.0.1
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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