unistdio/*printf: Fix negative width handling for %U, %lU, %llU. * lib/vasnprintf.c (VASNPRINTF): In the code for %U, %lU, %llU, test for the FLAG_LEFT bit in the flags variable. * tests/unistdio/test-u8-printf1.h (test_xfunction): Add tests for width given as argument for the directives %U, %lU, %llU, %s, %a, %f, %e, %g. * tests/unistdio/test-u16-printf1.h (test_xfunction): Likewise. * tests/unistdio/test-u32-printf1.h (test_xfunction): Likewise. * tests/unistdio/test-ulc-printf1.h (test_xfunction): Likewise.