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)
(cherry picked from commit 50dc1ac1)

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