Support for RISC-V builds

[braydonf]

Attempted to build on strfry with RVA23 Spacemit K3 and SiFive U74 RISC-V cores and received the following error:

In file included from golpe/external/json/include/tao/json/events/../internal/number_state.hpp:13,
                 from golpe/external/json/include/tao/json/events/../internal/action.hpp:16,
                 from golpe/external/json/include/tao/json/events/from_file.hpp:7,
                 from golpe/external/json/include/tao/json/from_file.hpp:9,
                 from golpe/external/json/include/tao/json.hpp:11:
golpe/external/json/include/tao/json/events/../internal/../external/double.hpp:77:2: error: #error Target architecture was not detected as supported by Double-Conversion.
   77 | #error Target architecture was not detected as supported by Double-Conversion.
      |  ^~~~~
make: *** [golpe/rules.mk:32: golpe/logging.o] Error 1
make: *** Waiting for unfinished jobs....
make: *** [golpe/rules.mk:32: build/main.o] Error 1
make: *** [golpe/rules.mk:32: src/Decompressor.o] Error 1
make: *** [golpe/rules.mk:32: build/config.o] Error 1

There may be other errors; however, this was the first and possibly only one. Might be a simple fix?