Resolve some issues to build on mac.

This includes renaming Fifo.bsv to Fifos.bsv to account for a case insensitive file system which confuses this library with FIFO.bsv.
Also this includes an update of the verilator flags that are needed for modern verilator.
Finally, some verilator flag changes for building with LLVM.

src_Core/CPU/CsrFile.bsv

@@ -29,7 +29,7 @@ import DefaultValue::*;
 import ConcatReg::*;
 import ConfigReg::*;
 import Ehr::*;
-import Fifo::*;
+import Fifos::*;
 import Vector::*;
 import FIFO::*;
 import GetPut::*;