strtoll: Work around a bug on native Windows and Minix. * lib/stdlib.in.h (strtoll): Override if REPLACE_STRTOLL is 1. * m4/stdlib_h.m4 (gl_STDLIB_H_DEFAULTS): Initialize REPLACE_STRTOLL. * m4/strtoll.m4 (gl_FUNC_STRTOLL): Test whether strtoll works. Set REPLACE_STRTOLL. * modules/stdlib (Makefile.am): Substitute REPLACE_STRTOLL. * modules/strtoll (configure.ac): Test REPLACE_STRTOLL. * tests/test-strtoll.c (main): Add tests of hexadecimal integer syntax. * doc/posix-functions/strtoll.texi: Mention the bug.