sigdescr_np for SIGEMT is useless

[Bruno Haible]

The function sigdescr_np is supposed to "return the message describing the
signal signum" [1].

However, for the value SIGEMT, it returns a string without real information.
If a user did not know what SIGEMT means before, he won't know it afterwards.

How to reproduce:
$ gcc -Wall foo.c
$ ./a.out
SIGEMT -> EMT trap

Suggestion: Use the description string "Instruction emulation needed" instead.
That's what is understandable from the FreeBSD man page [2].

Seen on Debian GNU/Hurd, with glibc 2.34.

[1] https://www.gnu.org/software/libc/manual/html_node/Signal-Messages.html
[2] https://www.freebsd.org/cgi/man.cgi?sektion=3&query=signal