config: change name of default build dir

'targets' is not really meaningfull.
'build' means what it means.
'.build' just hides it as well! :-)

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

reporter_name="Ioannis E. VENETIS"

reporter_url="http://sourceware.org/ml/crossgcc/2009-11/msg00109.html"

reporter_comment=""