compiler: fix checkNonStdWay for targets that require dynamic libraries

This commit fixes checkNonStdWay to ensure that for targets whose RTS
linker can only load dynamic code, the dynamic way of object is
selected.

(cherry picked from commit 94ef949e)
(cherry picked from commit 38474be0)

compiler/GHC/Linker/Deps.hs

@@ -59,6 +59,7 @@ import System.Directory
 
 data LinkDepsOpts = LinkDepsOpts
   { ldObjSuffix   :: !String                        -- ^ Suffix of .o files
+  , ldForceDyn    :: !Bool                          -- ^ Always use .dyn_o?
   , ldOneShotMode :: !Bool                          -- ^ Is the driver in one-shot mode?
   , ldModuleGraph :: !ModuleGraph
   , ldUnitEnv     :: !UnitEnv
@@ -351,6 +352,16 @@ throwProgramError opts doc = throwGhcExceptionIO (ProgramError (renderWithContex
 
 checkNonStdWay :: LinkDepsOpts -> Interp -> SrcSpan -> IO (Maybe FilePath)
 checkNonStdWay _opts interp _srcspan
+  -- On some targets (e.g. wasm) the RTS linker only supports loading
+  -- dynamic code, in which case we need to ensure the .dyn_o object
+  -- is picked (instead of .o which is also present because of
+  -- -dynamic-too)
+  | ldForceDyn _opts = do
+      let target_ways = fullWays $ ldWays _opts
+      pure $ if target_ways `hasWay` WayDyn
+        then Nothing
+        else Just $ waysTag (WayDyn `addWay` target_ways) ++ "_o"
+
   | ExternalInterp {} <- interpInstance interp = return Nothing
     -- with -fexternal-interpreter we load the .o files, whatever way
     -- they were built.  If they were built for a non-std way, then

compiler/GHC/Linker/Loader.hs

@@ -639,6 +639,7 @@ initLinkDepsOpts hsc_env = opts
   where
     opts = LinkDepsOpts
             { ldObjSuffix   = objectSuf dflags
+            , ldForceDyn    = sTargetRTSLinkerOnlySupportsSharedLibs $ settings dflags
             , ldOneShotMode = isOneShot (ghcMode dflags)
             , ldModuleGraph = hsc_mod_graph hsc_env
             , ldUnitEnv     = hsc_unit_env hsc_env