A long time ago in glibc, repertoire maps were used (but they
were removed already in 2000), those mapping files were named
as mnemonics, so "mnemonic" is a term that would almost
certainly come up if somebody studies glibc side (perhaps even
the related standards like ISO 9945 [which I don't have access
to]) so I thought it's worth to mention to term in the man page
to make sure we're talking about the same thing, otherwise
someone might wonder is that something different or not.
IOW, symbolic names and mnemonics are often used interchangeably,
let's mention the other often used term in the page, too.
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>