Build fails on macOS with duplicate symbol definitions

[jvnknvlgl]

From the logs:

ghc-9.6.6: Symbol __Z47VVexRiscv_VexRiscv___nba_comb__TOP__VexRiscv__0P18VVexRiscv_VexRiscv has no Global Offset Table address!

ghc-9.6.6: Failed to lookup symbol: __Z47VVexRiscv_VexRiscv___nba_comb__TOP__VexRiscv__0P18VVexRiscv_VexRiscv
ghc-9.6.6: Failed to lookup symbol: __Z30VVexRiscv___024root___eval_icoP19VVexRiscv___024root
ghc-9.6.6: Failed to lookup symbol: __Z26VVexRiscv___024root___evalP19VVexRiscv___024root
GHC runtime linker: fatal error: I found a duplicate definition for symbol
   __ZNKSt3__112basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEE20__throw_length_errorB8ne180100Ev
whilst processing object file
   /Users/jvnknvlgl/Projects/clash-vexriscv/clash-vexriscv/build_out_dir/libVexRiscvFFI.a
The symbol was previously defined in
   /Users/jvnknvlgl/Projects/clash-vexriscv/clash-vexriscv/build_out_dir/libVexRiscvFFI.a(#1:VVexRiscv.o)
This could be caused by:
   * Loading two different object files which export the same symbol
   * Specifying the same object file twice on the GHCi command line
   * An incorrect `package.conf' entry, causing some object to be
     loaded twice.

And then several times more for different symbol names. GHC is at version 9.6.6 and Verilator reports to be at version 5.028, the C(XX) compiler is the default compiler that is shipped with Xcode on macOS which is Clang 16.0.0.

Initially, I also encountered a build failure due to macOS apparently using a very old default version of C++, this can be resolved by adding --std=c++14 (or higher, probably) to FFI_CPPFLAGS in clash-vexriscv/Makefile.