Clang used to support [[nodebug]] everywhere except on typedefs. Since
we don't support such old Clangs anymore, we can get rid of _LIBCPP_NODEBUG_TYPE
in favour of always using _LIBCPP_NODEBUG.
Differential Revision: https://reviews.llvm.org/D108996
This started as fixing a typo in a ADDITIONAL_COMPILE_FLAGS directive
which turned out to uncover a few places where we warned about signedness
changes.
As a fly-by fix, this updates the various __advance overloads
for style consistency.
Differential Revision: https://reviews.llvm.org/D106372