sim/erc32: fix gdb with simulator build

sim/erc32: fix gdb with simulator build

In commit:

  commit 7b01c1cc1d111ba0afa51e60fa9842d3b971e2d1
  Date:   Mon Apr 4 22:38:04 2022 +0100

      sim: fixes for libopcodes styled disassembler

changes were made to the simulator source to handle the new libopcodes
disassembler styling API.

Unfortunately, these changes broke building GDB with the erc32 (sparc)
simulator, like this:

  ../src/configure --target=sparc-linux
  make all-gdb
  ....
  /usr/bin/ld: ../sim/erc32/libsim.a(interf.o): in function `sim_open':
  /tmp/build/sim/../../src/sim/erc32/interf.c:247: undefined reference to `fprintf_styled'
  collect2: error: ld returned 1 exit status

The problem is that in commit 7b01c1cc1d11 the fprintf_styled function
was added into sis.c.  This file is only used when building the 'run'
binary, that is, the standalone simulator, and is not included in the
libsim.a library.

Now, the obvious fix would be to move fprintf_styled into libsim.a,
however, that turns out to be tricky.

The erc32 simulator currently has two copies of the function run_sim,
one in sis.c, and one in interf.c, both of these copies are global.

Currently, the 'run' binary links fine, though I suspect this might be
pure luck.  When I tried moving fprintf_styled into interf.c, I ran
into multiple-definition (of run_sim) errors.  I suspect that by
requiring the linker to pull in fprintf_styled from libsim.a I was
changing the order in which symbols were loaded, and the linker was
now seeing both copies of run_sim, while currently we only see one
copy.

The ideal solution of course, would be to merge the two similar, but
slightly different copies of run_sim, and just use the one copy.  Then
we could safely move fprintf_styled into interf.c too, and all would
be good.

But I don't have time right now to start debugging the erc32
simulator, so I wanted a solution that fixes the build without
introducing multiple definition errors.

The easiest solution I think is to just have two copies of
fprintf_styled, one in sis.c, and one in interf.c.  Unlike run_sim,
these two copies are both static, so we will not run into multiple
definition issues with this function.  The functions themselves are
not very big, so it's not a huge amount of duplicate code.

I am very aware that this is not an ideal solution, and I would
welcome anyone who wants to take on fixing the run_sim problem
properly, and then cleanup the fprintf_styled duplication.