tools: bootstrap: remove non-digits from minor version

libtool is notoriously known to have been patched over the time and was
provided as 2.4.7-dirty on archlinux, which makes the integer comparison
test fail since 7-dirty is not an integer.

extras/tools/bootstrap

@@ -22,7 +22,7 @@ check_version() {
     gotver=$2
     gotmajor=`echo $gotver|cut -d. -f1`
     gotminor=`echo $gotver|cut -d. -f2`
-    gotmicro=`echo $gotver|cut -d. -f3`
+    gotmicro=`echo $gotver|cut -d. -f3|tr -c -d '[:digit:]'`
     [ -z "$gotmicro" ] && gotmicro=0
     needmajor=`echo $3|cut -d. -f1`
     needminor=`echo $3|cut -d. -f2`