*: require semicolon after DEFINE_MTYPE & co

*: require semicolon after DEFINE_MTYPE & co

Back when I put this together in 2015, ISO C11 was still reasonably new
and we couldn't require it just yet.  Without ISO C11, there is no
"good" way (only bad hacks) to require a semicolon after a macro that
ends with a function definition.  And if you added one anyway, you'd get
"spurious semicolon" warnings on some compilers...

With C11, `_Static_assert()` at the end of a macro will make it so that
the semicolon is properly required, consumed, and not warned about.

Consistently requiring semicolons after "file-level" macros matches
Linux kernel coding style and helps some editors against mis-syntax'ing
these macros.

Signed-off-by: David Lamparter <equinox@diac24.net>