build: avoid files generated by doxygen starting with _2
build: avoid files generated by doxygen starting with _2

Github was failing to show it so all example links were broken.

Signed-off-by: Bruno Dilly <ea4fb6320c1221b6a559089d8ab97ffc53fc6586@intel.com>

bsmelo/soletta,brunobottazzini/soletta,wzhen12/soletta,bsmelo/soletta,dorileo/soletta,lpereira/soletta,lpereira/soletta,lpereira/soletta,bsmelo/soletta,dorileo/soletta,edersondisouza/soletta,edersondisouza/soletta,wzhen12/soletta,dorileo/soletta,brunobottazzini/soletta,brunobottazzini/soletta,bsmelo/soletta,bsmelo/soletta,edersondisouza/soletta,wzhen12/soletta,brunobottazzini/soletta,dorileo/soletta,lpereira/soletta,wzhen12/soletta,edersondisouza/soletta,edersondisouza/soletta,edersondisouza/soletta,dorileo/soletta,brunobottazzini/soletta,wzhen12/soletta,brunobottazzini/soletta,lpereira/soletta,dorileo/soletta,bsmelo/soletta,wzhen12/soletta