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'.

# Suppress a valgrind message about use of uninitialized memory in strchrnul().
# This use is OK because it provides only a speedup.
{
    strchrnul-value4
    Memcheck:Value4
    fun:strchrnul
}
{
    strchrnul-value8
    Memcheck:Value8
    fun:strchrnul
}