Fix #3182: 64 bit FP value returned by C calls was getting trashed

   movss instruction was being used to move the result into the 
   destination register instead of movsd

compiler/nativeGen/X86/CodeGen.hs

@@ -1779,7 +1779,7 @@ genCCall target dest_regs args = do
 	assign_code [CmmHinted dest _hint] = 
 	  case typeWidth rep of
 		W32 | isFloatType rep -> unitOL (MOV (floatSize W32) (OpReg xmm0) (OpReg r_dest))
-		W64 | isFloatType rep -> unitOL (MOV (floatSize W32) (OpReg xmm0) (OpReg r_dest))
+		W64 | isFloatType rep -> unitOL (MOV (floatSize W64) (OpReg xmm0) (OpReg r_dest))
 		_ -> unitOL (MOV (cmmTypeSize rep) (OpReg rax) (OpReg r_dest))
 	  where 
 		rep = localRegType dest