New comment by ev-ermakov on void-packages repository

https://github.com/void-linux/void-packages/pull/26228#issuecomment-724130344

Comment:
The following code block should be added:
```sh
pre_build() {
	export BITCOIN_GENBUILD_NO_GIT=1
}
```

And just a little cosmetic change:
```diff
-		vinstall contrib/${b}.bash-completion 644 usr/share/bash-completion $b
+		vcompletion contrib/${b}.bash-completion bash $b
```