Allow to set arbitrary extra compiler flags from outside (usefull for supporting case when we need to disable x509 linking). Also by default do NOT link agains x509 / mbedtls.

See merge request nexedi/osie!13

In virtual mode we can NOT read digital / analog IN at all. Thus prevent segfault from reading from uninitialized address.

See merge request !12

Test: Program is tested locally with laptop.

        modified:   server.c

Test: Program is tested locally with laptop.

        modified:   server.c

Test: Program is tested locally with laptop.

        modified:   server.c

Test: Program is tested locally with laptop.

        modified:   server.c

See merge request !11

Username / Passwords are dynamic variables we got from command line and not constantants. Thus adjust.