@BuZz all right, bought a new one, waiting for it to arrive.

but the "flash" signal shouldn't be appearing then?

thx for the help, finally got it compiled, but it mostly just crashes back to retroarch 10 seconds into startup on the games I wanted it for. ahh, well, that's why it's called experimental.

Ok Guys... today building went fine \o/ I trust the root cause was overheating. In fact we suffered from an impressive heatwave over there and like me my pi didn't enjoy it!!! I do confirm: I've changed nothing compare to yesterday (despite my low disk space, power plug and "lower" overclock settings :p)

I feel better now first because the air temperature is way more acceptable for a human being (and for the pi). Second because my setup is not at fault and I know that I got an up to date and proper raspbian version. All good news. Thanks a lot for the support and sorry for that post, useless in fact :(