Need option to use system gcc and binutils on Windows/msys2

Hi,

Trying to build GHC 7.8.2 from sources on Windows 7, from msys2 shell, required binaries such as gcc, ld, ar are forced to those in inplace directories (windows-extra), even system/env provide such tools (e.g. using pacman package manager in msys2): https://ghc.haskell.org/trac/ghc/browser/ghc/configure.ac#L274 .

It leads to issues as tools in inplace are quite old.

Particularly it can be critical about linking: GHC will be working with old ld, but you can have built/linked libraries using the more recent ld. Then, what's built using system tool can't be used throught GHC (ld version conflict).

Trac metadata

Trac field	Value
Version	7.8.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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