ghc-bin: enforce dynamic way when the target requires so

This commit makes ghc-bin use dynamic way when it is doing interactive
stuff on certain targets whose RTS linker can only handle dynamic
code.

(cherry picked from commit 88e99248)

ghc/Main.hs

@@ -224,9 +224,26 @@ main' postLoadMode units dflags0 args flagWarnings = do
 
         -- The rest of the arguments are "dynamic"
         -- Leftover ones are presumably files
-  (dflags3, fileish_args, dynamicFlagWarnings) <-
+  (dflags3', fileish_args, dynamicFlagWarnings) <-
       GHC.parseDynamicFlags logger2 dflags2 args'
 
+  -- When we do ghci, force using dyn ways if the target RTS linker
+  -- only supports dynamic code
+  let dflags3
+        | LinkInMemory <- link,
+          sTargetRTSLinkerOnlySupportsSharedLibs $ settings dflags3'
+            = setDynamicNow $
+              -- See checkOptions below, -fexternal-interpreter is
+              -- required when using --interactive with a non-standard
+              -- way (-prof, -static, or -dynamic).
+              setGeneralFlag' Opt_ExternalInterpreter $
+              -- Use .o for dynamic object, otherwise it gets dropped
+              -- with "Warning: ignoring unrecognised input", see
+              -- objish_suffixes
+              dflags3' { dynObjectSuf_ = objectSuf dflags3' }
+        | otherwise
+            = dflags3'
+
   let dflags4 = if backendNeedsFullWays bcknd &&
                    not (gopt Opt_ExternalInterpreter dflags3)
                 then