mount: add fallback for versionsort()

mount: add fallback for versionsort()

I was trying to build util-linux-ng on uclibc and it failed

| lomount.c: In function 'looplist_next':
| lomount.c:223: error: 'versionsort' undeclared (first use in this function)
| lomount.c:223: error: (Each undeclared identifier is reported only once
| lomount.c:223: error: for each function it appears in.)
| make[2]: *** [mount-lomount.o] Error 1
|

which is understood because versionsort is GNU extension and uclibc does
not implement it.

Reported-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Karel Zak <kzak@redhat.com>