xbps-src: introduce XBPS_STATEDIR to store state files, logs and others.

XBPS_STATEDIR is created in XBPS_BUILDDIR/.xbps-${sourcepkg}-${version}
and contains logs and state files for all phases, as well as wrappers.

We can now inspect the output from all hooks.

common/hooks/do-pkg/00-gen-pkg.sh

@@ -42,8 +42,8 @@ genpkg() {
 	if [ -s ${PKGDESTDIR}/shlib-requires ]; then
 		_shrequires="$(cat ${PKGDESTDIR}/shlib-requires)"
 	fi
-	if [ -s ${wrksrc}/.xbps_${sourcepkg}_git_revs ]; then
-		_gitrevs="$(cat ${wrksrc}/.xbps_${sourcepkg}_git_revs)"
+	if [ -s ${XBPS_STATEDIR}/gitrev ]; then
+		_gitrevs="$(cat ${XBPS_STATEDIR}/gitrev)"
 	fi
 
 	if [ -n "$provides" ]; then