Detect tools before cleaning in ./configure
Detect tools before cleaning in ./configure

Previously this script would first try to run `ruby -S rake clean`. The `rake`
command here was pulled from the `@rake` instance variable. Due to this
variable not being set by default at this point the resulting command would be
`ruby -S clean` instead, resulting in a load error.

This commit fixes this by first checking the tools used and *then* running a
clean.

This fixes #2915.

mlarraz/rubinius,jemc/rubinius,benlovell/rubinius,digitalextremist/rubinius,benlovell/rubinius,digitalextremist/rubinius,ruipserra/rubinius,jemc/rubinius,benlovell/rubinius,benlovell/rubinius,heftig/rubinius,Azizou/rubinius,jsyeo/rubinius,dblock/rubinius,Azizou/rubinius,Wirachmat/rubinius,dblock/rubinius,Azizou/rubinius,benlovell/rubinius,jemc/rubinius,ruipserra/rubinius,kachick/rubinius,kachick/rubinius,Azizou/rubinius,ruipserra/rubinius,mlarraz/rubinius,heftig/rubinius,heftig/rubinius,jemc/rubinius,jemc/rubinius,sferik/rubinius,dblock/rubinius,Wirachmat/rubinius,ngpestelos/rubinius,ngpestelos/rubinius,Azizou/rubinius,digitalextremist/rubinius,jsyeo/rubinius,mlarraz/rubinius,kachick/rubinius,Wirachmat/rubinius,dblock/rubinius,Wirachmat/rubinius,Azizou/rubinius,jsyeo/rubinius,Azizou/rubinius,heftig/rubinius,mlarraz/rubinius,heftig/rubinius,heftig/rubinius,Wirachmat/rubinius,mlarraz/rubinius,ngpestelos/rubinius,digitalextremist/rubinius,kachick/rubinius,sferik/rubinius,jemc/rubinius,ruipserra/rubinius,sferik/rubinius,jsyeo/rubinius,kachick/rubinius,digitalextremist/rubinius,sferik/rubinius,dblock/rubinius,ngpestelos/rubinius,ngpestelos/rubinius,mlarraz/rubinius,jemc/rubinius,ngpestelos/rubinius,mlarraz/rubinius,sferik/rubinius,benlovell/rubinius,heftig/rubinius,digitalextremist/rubinius,ruipserra/rubinius,sferik/rubinius,jsyeo/rubinius,jsyeo/rubinius,dblock/rubinius,ngpestelos/rubinius,kachick/rubinius,Wirachmat/rubinius,Wirachmat/rubinius,ruipserra/rubinius,kachick/rubinius,sferik/rubinius,dblock/rubinius,jsyeo/rubinius,digitalextremist/rubinius,kachick/rubinius,benlovell/rubinius,ruipserra/rubinius