duplicate symbol '_bitbang_swd'

Building on macOS yields the following error:
```
duplicate symbol '_bitbang_swd' in:
src/.libs/libopenocd.a(libocdjtagdrivers_la-remote_bitbang.o)
src/.libs/libopenocd.a(libocdjtagdrivers_la-bitbang.o)
ld: 1 duplicate symbol for architecture x86_64
collect2: error: ld returned 1 exit status
make[2]: *** [src/openocd] Error 1
make[1]: *** [all-recursive] Error 1
make: *** [all] Error 2
```
Updating `riscv-openocd` solves this issue, but introduces new ones.

Start with the macOS build output and inspect the two archive objects, libocdjtagdrivers_la-remote_bitbang.o and libocdjtagdrivers_la-bitbang.o, named in the linker error. Review the riscv-openocd update mentioned in the issue, then verify that make all completes without the duplicate symbol or the newer reported failures.

Written by the indexing model from the issue text.