Well you are right to ask, if you do not know the project....
you can do additional checks:
http://www.virustotal.com/or google for online scans
But as others pointed out, there are regular false positives.
gdb (the debugger) can cause them, as like every debugger, it needs to intercept the debugged process. Intercepting another process is more or less what a virus does too. except the debugger does it with your permission and knowledge...
upx (an executable packer). it packs your executable code. So it has routines that can modify the code. Some viruses do that. viruses do it for encryption, so the code can not be seen/scanned that easily.