Fix stage2 build on ARM.

LLVM supports PIC on ARM from what I can see.
Signed-off-by: Austin Seipp <aseipp@pobox.com>

compiler/main/DynFlags.hs

@@ -3406,6 +3406,7 @@ makeDynFlagsConsistent dflags
         in loop dflags' warn
  | hscTarget dflags == HscLlvm &&
    not ((arch == ArchX86_64) && (os == OSLinux || os == OSDarwin)) &&
+   not ((isARM arch) && (os == OSLinux)) &&
    (not (gopt Opt_Static dflags) || gopt Opt_PIC dflags)
     = if cGhcWithNativeCodeGen == "YES"
       then let dflags' = dflags { hscTarget = HscAsm }

compiler/utils/Platform.hs

@@ -10,6 +10,7 @@ module Platform (
         ArmABI(..),
 
         target32Bit,
+        isARM,
         osElfTarget,
         platformUsesFrameworks,
 )
@@ -54,6 +55,9 @@ data Arch
         | ArchMipsel
         deriving (Read, Show, Eq)
 
+isARM :: Arch -> Bool
+isARM (ArchARM {}) = True
+isARM _ = False
 
 -- | Operating systems that the native code generator knows about.
 --      Having OSUnknown should produce a sensible default, but no promises.