These were uncovered when trying to run `bootstrap.sh` with Autoconf
2.71:
* AC_CONFIG_HEADER() is deprecated in favor of AC_CONFIG_HEADERS().
* AC_HEADER_TIME is obsolete.
* $as_echo is deprecated in favor of AS_ECHO() which requires an update
to ax_pthread.m4.
Note that the generated artifacts in this commit are from Autoconf 2.69.
Resolves#139
(cherry picked from commit 21d3c4ae58)
Updated the macro-set autoconf/ax_pthread.m4 to its latest upstream version.
ASTERISK-26046 #close
Change-Id: I11abc11d17acd2b6a8a5a5be8ae8e0949dab9cc7