*printf-posix: Fix implementation of %b directive. * lib/vasnprintf.c (VASNPRINTF): In the %b directive implementation, fix the precision handling, and ignore the '0' flag when a width and a precision are both present. * tests/test-snprintf-posix.h (test_function): Add test cases for the %x directive and more test cases for the %b directive. * tests/test-sprintf-posix.h (test_function): Likewise. * tests/test-vasnprintf-posix.c (test_function): Likewise. * tests/test-vasnwprintf-posix.c (test_function): Likewise. * tests/test-vasprintf-posix.c (test_function): Likewise. * modules/vasnwprintf-posix-tests (Files): Add m4/musl.m4. (configure.ac): Invoke gl_MUSL_LIBC.