Use std::signed_integral concept

...which, unlike std::is_signed, also requires that T is an integer type, not
just any arithmetic type, but which appears to fit well here anyway.

But LLVM 12 libc++, which is apparently used by Android builds, only provides a
bare-bones <concepts> that lacks std::signed_integral (among others), so for now
introduce o3tl/concepts.hxx providing what's missing (incl. std::integral and
std::unsigned_integral, for some kind of consistency).

Change-Id: I1c37d37fa1b57b5e3bf24c9e44f3973003905cb2
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/158406
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

0 files changed, 0 insertions, 0 deletions