[LTP] Rewrite fmtmsg01.c

[Petr Vorel]

Hi,

I'm going to rewrite testcases/kernel/syscalls/fmtmsg/fmtmsg01.c which tests
addseverity() and fmtmsg(). The reason is that addseverity() is not POSIX,
thus not in musl. Taking an usual approach (*) is not enough, because the test
logic depends on all tests being run. Thus just hope the test is valid (thus
worth of cleanup).

(*) check with autotools whether addseverity() available and comment out parts
which test it; + TCONF test if fmtmsg() is not available - uclibc.

Kind regards,
Petr