With RISC-V being a relatively young toolchain, a lot of inconsistencies
between different toolchains are to be found that differ in the target
triple and the flags supported. This build system performs run-time
tests to detect the toolchain and supported flags.
With `BUILD_IN_DOCKER=1` issues arise, as this checks are performed
outside of the docker container. However, the host may have no RISC-V
toolchain installed or a different toolchain, so there is little reason
in performing this detection then. Instead, a hard coded target triple
and supported flags are provided when using `BUILD_IN_DOCKER=1`.
e0a81fe945