MINOR: fd: Use closefrom() as my_closefrom() if supported.

Add a new option, USE_CLOSEFROM. If set, it is assumed the system provides
a closefrom() function, so use it.
It is only implicitely used on FreeBSD for now, it should work on
OpenBSD/NetBSD/DragonflyBSD/Solaris too, but as I have no such system to
test it, I'd rather leave it disabled by default. Users can add USE_CLOSEFROM
explicitely on their make command line to activate it.
2 files changed