Prevent -optc arguments from being duplicated in reverse order (#17471)

This reverts a part of commit
7bc5d6c6 that causes all arguments
to `-optc` (and `-optcxx`) to be passed twice to the C/C++ compiler,
once in reverse order and then again in the correct order. While
passing duplicate arguments is usually harmless it can cause breakage
in this pattern, which is employed by Hackage libraries in the wild:

```
ghc Foo.hs foo.c -optc-D -optcFOO
```

As `FOO -D -D FOO` will cause compilers to error.

Fixes #17471.

(cherry picked from commit 9a896a55)

compiler/main/SysTools/Tasks.hs

@@ -127,10 +127,9 @@ runCc mLanguage dflags args = traceToolCommand dflags "cc" $ do
     Nothing -> ([], userOpts_c)
     Just language -> ([Option "-x", Option languageName], opts)
       where
-        s = settings dflags
         (languageName, opts) = case language of
-          LangC      -> ("c",             sOpt_c s ++ userOpts_c)
-          LangCxx    -> ("c++",           sOpt_cxx s ++ userOpts_cxx)
+          LangC      -> ("c",             userOpts_c)
+          LangCxx    -> ("c++",           userOpts_cxx)
           LangObjc   -> ("objective-c",   userOpts_c)
           LangObjcxx -> ("objective-c++", userOpts_cxx)
           LangAsm    -> ("assembler",     [])

testsuite/tests/ffi/should_run/T17471.hs

+{-# LANGUAGE ForeignFunctionInterface #-}
+module Main where
+
+import Foreign.C.Types
+
+foreign import ccall "foo" foo :: IO CInt
+
+main :: IO ()
+main = foo >>= print

testsuite/tests/ffi/should_run/T17471.stdout

+1

testsuite/tests/ffi/should_run/T17471_c.c

+int foo() {
+#if defined(FOO)
+  return 1;
+#else
+  return 0;
+#endif
+}

testsuite/tests/ffi/should_run/all.T

@@ -213,3 +213,6 @@ test('PrimFFIWord16', [omit_ways(['ghci'])], compile_and_run, ['PrimFFIWord16_c.
 test('T493', [omit_ways(['ghci'])], compile_and_run, ['T493_c.c'])
 
 test('UnliftedNewtypesByteArrayOffset', [omit_ways(['ghci'])], compile_and_run, ['UnliftedNewtypesByteArrayOffset_c.c'])
+
+test('T17471', [omit_ways(['ghci'])], compile_and_run,
+     ['T17471_c.c -optc-D -optcFOO'])