stdio-common: Add tests for formatted asprintf output specifiers

stdio-common: Add tests for formatted asprintf output specifiers

Wire asprintf into test infrastructure for formatted printf output
specifiers.

Owing to mtrace logging of lots of memory allocation calls these tests
take a considerable amount of time to complete, except for the character
conversion, taking from 00m20s for 'tst-printf-format-as-s --direct s',
through 01m10s and 03m53s for 'tst-printf-format-as-char --direct i' and
'tst-printf-format-as-double --direct f' respectively, to 19m24s for
'tst-printf-format-as-ldouble --direct f', all in standalone execution
from NFS on a RISC-V FU740@1.2GHz system and with output redirected over
100Mbps network via SSH.  It is with the skeleton's stub implementation
of dladdr(3); execution times with regular dladdr(3) are up to over
twice longer.

Set timeouts for the tests accordingly then, with a global default for
all the asprintf tests, and then individual higher settings for double
and long double tests each.

Reviewed-by: DJ Delorie <dj@redhat.com>