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="Remy Bohmer"

 reporter_url="linux@bohmer.net"

 reporter_comment="Example for building a toolchain for m68000 bare metal targets"