This reverts commit f2583f3acf596cc545c8c0e3cb28e712f4ebf21b.
There is a large body of non-conforming C-like code using format strings
like this:
#define PRIuS "zu"
void h(size_t foo, size_t bar) {
printf("foo is %"PRIuS", bar is %"PRIuS, foo, bar);
}
Rejecting this code would be very disruptive. We could decide to do
that, but it's sufficiently disruptive that I think it requires
gathering more community consensus with an RFC, and Aaron indicated [1]
it's OK to revert for now so continuous testing systems can see past
this issue while we decide what to do.
[1] https://reviews.llvm.org/D153156#4607717
declaration.
Names starting with an underscore are reserved at the global scope, so
cannot be used as the name of an extern "C" symbol in any scope because
such usages conflict with a name at global scope.
Also do not warn on `#define _foo` or `#undef _foo`.
Only global scope names starting with _[a-z] are reserved, not the use
of such an identifier in any other context.
