Add experimental support for emulation of the Sprow ARM7TDMI co-processor.

[rjpontefract]

Add experimental support for emulation of the Sprow ARM7TDMI co-processor. This was ported from BeebEm so credit for the code goes to the BeebEm team. Many thanks to Robert Sprowson for permission to include the firmware with b-em.

[SteveFosdick]

I have merged this but when I built the merged version I got some warnings from gcc. The one about comments seems harmless enough but the other two looked significant:

sprow.c: In function ‘sprow_dbg_disassemble’:
sprow.c:273:3: warning: ‘strncpy’ output truncated before terminating nul copying as many bytes from a string as its length [-Wstringop-truncation]
  273 |   strncpy(buf, dest, strlen(dest));
      |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

and

ARMulator/armemu.c:841:24: warning: ‘do_int’ may be used uninitialized [-Wmaybe-uninitialized]
  841 |                     if (do_int && (cp14r0 & ARMul_CP14_R0_INTEN2))
      |                        ^
ARMulator/armemu.c:816:25: note: ‘do_int’ was declared here
  816 |                     int do_int = 0;
      |                         ^~~~~~

I have pushed fixes in commit https://github.com/stardot/b-em/commit/58e71860a7db660013b16130901046f9a6e62102 Could you check the one where I haved moved the initialisation of do_int. The issue here is that there is a goto into that block where the labels is after the initialisation which gcc seems to interpret as the initialisation not being done. Moving if after the label silences the warning.

[rjpontefract]

Those changes look fine to me. I built it with clang on macOS and got a different set of warnings. I'll build it with GCC and see if there's anything else that needs attention.