Load `pthreads` by default on Windows

The GCC Bindists that we use compile with `pthread` enabled by default.
This means that on every link the dll is passed as a dependency by the
driver. Lots of packages depend on it but the runtime linker doesn't
provide it by default making compiled code work but not interpreted.

Following D3028 `pthreads` would be provided by default ONLY when linked
dynamicly, which we don't support yet (See D2592). Until this is the
case we need to manually provide `libpthreads`.

Test Plan: ./validate

Reviewers: austin, hvr, bgamari

Reviewed By: bgamari

Subscribers: thomie, #ghc_windows_task_force

Differential Revision: https://phabricator.haskell.org/D3155

1 files changed, 13 insertions, 1 deletions

diff --git a/compiler/ghci/Linker.hs b/compiler/ghci/Linker.hs
index e89f1bb680..ebd27b0e33 100644
--- a/compiler/ghci/Linker.hs
+++ b/compiler/ghci/Linker.hs
@@ -312,7 +312,19 @@ linkCmdLineLibs' hsc_env pls =
                            , libraryPaths = lib_paths}) = hsc_dflags hsc_env
 
       -- (c) Link libraries from the command-line
-      let minus_ls = [ lib | Option ('-':'l':lib) <- cmdline_ld_inputs ]
+      let minus_ls_1 = [ lib | Option ('-':'l':lib) <- cmdline_ld_inputs ]
+
+      -- On Windows we want to add libpthread by default just as GCC would.
+      -- However because we don't know the actual name of pthread's dll we
+      -- need to defer this to the locateLib call so we can't initialize it
+      -- inside of the rts. Instead we do it here to be able to find the
+      -- import library for pthreads. See Trac #13210.
+      let platform = targetPlatform dflags
+          os       = platformOS platform
+          minus_ls = case os of
+                       OSMinGW32 -> "pthread" : minus_ls_1
+                       _         -> minus_ls_1
+
       libspecs <- mapM (locateLib hsc_env False lib_paths) minus_ls
 
       -- (d) Link .o files from the command-line