Non-issue: allow user to custom "go" command in makefile

[hidehalo]

TinySQL require "go" version 1.13.

I can't install [email protected] via "Homebrew" on my laptop, cauz it's abandoned at upstream.

Since that, I must download [email protected] manually from "go" website.

The point is, a lots user work on go version > 1.13, they must have multiple go versions executable command.

We should allow user to custom "go" command in "Makefile".

eg:

# which [email protected]
[email protected] version
go version go1.13.15 darwin/amd64

# which [email protected]
go version
go version go1.18.3 darwin/amd64

# env variable `GOCMD` use `[email protected]` replace to `[email protected]`
[email protected] make test-proj1
cd tablecodec && \
	[email protected] test

# no specific `GOCMD` is fine, we would use default command "go"
 make test-proj1
 cd tablecodec && \
	go test

[hidehalo]

@winoros @yanguwan PTAL, thx!