Load dependent dlls.

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`.

Unfortunately due to time constraints I can't set up the framework
required in `GHC` to do this before the feature freeze.

So I suggest this alternate implementation:
When we load a dll, also bring it's dependencies into scope of the
interpeter.

This has pros and cons. Pro is, we'll fix many packages on hackage which
specify just `-lstdc++`. Since this points to `libstdc++-6.dll` which
will bring `libgcc` into scope.

The downside is, we'll be more lenient than GCC, in that the interpreter
will link much easier since it has implicit dependencies in scope.
Whereas for compilation to work you will have to specify it as an
argument to GHC.

This will make the Windows runtime linker more consistent with the unix
ones. The difference in semantics came about because of the differences
between `dlsym` and `GetProcAddress`.  The former seems to search the
given library and all it's dependencies, while the latter only searches
the export table of the library. So we need some extra manual work to
search the dependencies which this patch provides.

Test Plan:
```
./validate
```
```
$ echo :q | inplace/bin/ghc-stage2.exe --interactive +RTS -Dl -RTS
-lstdc++ 2>&1 | grep "Loading dependency"
```

```
$ echo :q | ../inplace/bin/ghc-stage2.exe --interactive -lstdc++ +RTS
-Dl -RTS 2>&1 | grep "Loading dependency"
Loading dependency *.exe -> GDI32.dll.
Loading dependency GDI32.dll -> ntdll.dll.
Loading dependency *.exe -> KERNEL32.dll.
Loading dependency KERNEL32.dll -> KERNELBASE.dll.
Loading dependency *.exe -> msvcrt.dll.
Loading dependency *.exe -> SHELL32.dll.
Loading dependency SHELL32.dll -> USER32.dll.
Loading dependency USER32.dll -> win32u.dll.
Loading dependency *.exe -> WINMM.dll.
Loading dependency WINMM.dll -> WINMMBASE.dll.
Loading dependency *.exe -> WSOCK32.dll.
Loading dependency WSOCK32.dll -> WS2_32.dll.
Loading dependency WS2_32.dll -> RPCRT4.dll.
Loading dependency libstdc++-6.dll -> libwinpthread-1.dll.
Loading dependency libstdc++-6.dll -> libgcc_s_seh-1.dll.
```

Trac tickets: #13093, #13189

Reviewers: simonmar, rwbarton, austin, bgamari, erikd

Reviewed By: bgamari

Subscribers: rwbarton, RyanGlScott, thomie, #ghc_windows_task_force

Differential Revision: https://phabricator.haskell.org/D3028

1 files changed, 0 insertions, 4 deletions

diff --git a/testsuite/tests/ghci/linking/Makefile b/testsuite/tests/ghci/linking/Makefile
index f8c5e19ce8..793152d68e 100644
--- a/testsuite/tests/ghci/linking/Makefile
+++ b/testsuite/tests/ghci/linking/Makefile
@@ -38,11 +38,7 @@ ghcilink002 :
 
 .PHONY: ghcilink003
 ghcilink003 :
-ifeq "$(WINDOWS)" "YES"
-	echo ":q" | "$(TEST_HC)" $(TEST_HC_OPTS_INTERACTIVE) -lstdc++-6
-else
 	echo ":q" | "$(TEST_HC)" $(TEST_HC_OPTS_INTERACTIVE) -lstdc++
-endif
 
 # Test 4: 
 #   package P