C coding

Define a no-op:
```
#define setfsuid(X) do {} while (0)
```

C compiling

Options

-Wall: turn all warning on.
-Werror : report warnings as errors.
-Wl,-no-undefined: unsure no symbol is undefined.

Autotools

The complete explanations about the dependencies between each input and output files are given in adl@gnu.org's autotools presentation.
Quoting is done using square brackets [this is quoted], that's why one cannot use if [ x$foo = x ]; use test instead.

GNU/kFreeBSD

Porting

setfsuid() (from <sys/fsuid.h>): Linux-specific.