[Sema] -Wformat: support C23 format specifier %b %B
Close #56885: WG14 N2630 added %b to fprintf/fscanf and recommended %B for
fprintf. This patch teaches -Wformat %b for the printf/scanf family of functions
and %B for the printf family of functions.
glibc 2.35 and latest Android bionic added %b/%B printf support. From
https://www.openwall.com/lists/libc-coord/2022/07/ no scanf support is available
yet.
Like GCC, we don't test library support.
GCC 12 -Wformat -pedantic emits a warning:
> warning: ISO C17 does not support the ‘%b’ gnu_printf format [-Wformat=]
The behavior is not ported.
Note: `freebsd_kernel_printf` uses %b differently.
Reviewed By: aaron.ballman, dim, enh
Differential Revision: https://reviews.llvm.org/
D131057