xbps-src: multiple performance improvements.

- use xbps-checkvers(1) to resolve dependencies.
- all dependencies are installed at once for the host and target.
- the `show-build-deps` target is now much faster.
- the `update-bulk/show-repo-updates` targets are now much faster.
- the `update-sys/show-sys-updates` targets are now much faster.
- the `bootstrap` target now works on musl hosts.
- simplified some loops.
- use cut(1) rather than awk(1) where applicable.
- multiple random changes to improve performance.

Based on work started by @Duncaen on https://github.com/void-linux/void-packages/pull/12433

Close https://github.com/void-linux/void-packages/pull/12433
Close https://github.com/void-linux/void-packages/pull/11282

.gitignore

@@ -7,3 +7,4 @@ masterdir*
 hostdir*
 etc/conf
 etc/virtual
+.xbps-checkvers.plist