strfmon_l: Fix -fsanitize=address finding. * lib/strfmon_l.c: Include <errno.h>, <stdbool.h>, <stdlib.h>, <string.h>. (MAX_ARGS): Renamed from MAX_ARG_WORDS. (directive_t, directives_t): New types. (fmon_parse): New function. (rpl_strfmon_l): Don't call va_arg more often than needed for the format string. Consume 'long double' arguments in places where the format string indicates so. * modules/strfmon_l (Depends-on): Add 'stdbool'.