🐛 RISCV64 Compilation not supported

[ifsheldon]

Describe the bug
RISC-V compilation is not supported, even though a minor change can unblock it. So, I'd make it a bug report, rather than a feature request.

To Reproduce
Steps to reproduce the behavior:

1. Download the official Golang toolchain for RISC-V
2. Set GOROOT_BOOTSTRAP to this go toolchain, e.g., $HOME/go
3. Manually execute the commands in https://github.com/cloudflare/cloudflared/blob/master/.teamcity/install-cloudflare-go.sh
4. Clone this repo
5. Set GOPATH to the compiled cloudflare-flavored go, e.g., /tmp/go
6. Run make cloudflared
7. Then we get an error This system's architecture riscv64 isn't supported from here

   cloudflared/Makefile

   Line 78 in 1f3e304

   $(error This system's architecture $(LOCAL_ARCH) isn't supported)

Expected behavior
Compiling from source for RISC-V machines is supported.

Environment and versions

• OS: Linux Debian
• Architecture: riscv64
• Version: master at 1f3e304

Simple Fix

I just appended two lines

else ifeq ($(LOCAL_ARCH),riscv64)
    TARGET_ARCH ?= riscv64

Then everything went smoothly and the compiled cloudflared worked great.

If you are willing to accept a PR, I can make one in no time.