configure: indent error/warning message

Indent the error/warning message so that it is explicit that
the second line is giving details for the first general hint.

Reported-by: Titus von Boxberg <titus@v9g.de>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

 reporter_name="Gustavo Zacarias <gustavo@zacarias.com.ar>"

 reporter_url="http://sourceware.org/ml/crossgcc/2011-03/msg00028.html"

 reporter_comment=""