This change requires introducing nsID::Clone(). Because it's infallible, the
patch also removes some redundant failure-handling code. (nsMemory::Clone() is
also infallible, so this code was redundant even before this change.)
Bug 1368932 removed MOZ_STATIC_ASSERT_VALID_ARG_COUNT because it didn't
actually work for large numbers of arguments. But it was kind of useful
for macros that expand to something broken when they are given no
variadic argument at all.
Now that we have a macro that doesn't require tricks to count empty
arguments lists, however, we can use straightforward static_asserts
instead of a generic macro, which has the side effect of providing more
context in the error message.
At the same time, remove the MOZ_STATIC_ASSERT_VALID_ARG_COUNT, which
doesn't actually work for more than 50 arguments(*), and which is now not
useful to detect 0 arguments.
(*) the build fails, but not directly thanks to the static_assert it
expands to.
