docs: use the error message in the known issues titles

This helps users find the appropriate known issue entry.

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

reporter_name="Alexander BIGGA"

reporter_url="http://sourceware.org/ml/crossgcc/2008-07/msg00000.html"

reporter_comment=""