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

common/xbps-src/libexec/build.sh

@@ -43,10 +43,6 @@ if [ "$PKGNAME" != "$XBPS_TARGET_PKG" -o -z "$XBPS_SKIP_DEPS" ]; then
     install_pkg_deps $PKGNAME $XBPS_TARGET_PKG pkg $XBPS_CROSS_BUILD $XBPS_CROSS_PREPARE || exit $?
 fi
 
-if [ -z "$XBPS_CROSS_PREPARE" ]; then
-    install_cross_pkg $XBPS_CROSS_BUILD || exit $?
-fi
-
 # Fetch distfiles after installing required dependencies,
 # because some of them might be required for do_fetch().
 $XBPS_LIBEXECDIR/xbps-src-dofetch.sh $SOURCEPKG $XBPS_CROSS_BUILD || exit 1