c-family: Support format checking C2X %b, %B formats

C2X adds a %b printf format to print integers in binary (analogous to
%x, including %#b printing a leading 0b on nonzero integers), with
recommended practice for a corresponding %B (where %#B uses 0B instead
of 0b) where that doesn't conflict with existing implementation
extensions.  See N2630 for details (accepted for C2X, not yet in the
latest working draft).  There is also a scanf %b format.

Add corresponding format checking support (%b accepted by -std=c2x
-Wformat -pedantic, %B considered an extension to be diagnosed with
-Wformat -pedantic).  glibc support for the printf formats has been
proposed at
<https://sourceware.org/pipermail/libc-alpha/2021-October/131764.html>
(scanf support to be done in a separate patch).

Note that this does not add any support for these formats to the code
for bounding the amount of output produces by a printf function,
although that would also be useful.

Bootstrapped with no regressions for x86_64-pc-linux-gnu.

gcc/c-family/
	* c-format.c (print_char_table): Add %b and %B formats.
	(scan_char_table): Add %b format.
	* c-format.h (T2X_UI, T2X_UL, T2X_ULL, T2X_US, T2X_UC, T2X_ST)
	(T2X_UPD, T2X_UIM): New macros.

gcc/testsuite/
	* gcc.dg/format/c11-printf-1.c, gcc.dg/format/c11-scanf-1.c,
	gcc.dg/format/c2x-printf-1.c, gcc.dg/format/c2x-scanf-1.c,
	gcc.dg/format/ext-9.c, gcc.dg/format/ext-10.c: New tests.

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