This change adds a new m4 macro AX_CHECK_A2X_TO_MANPAGE that
invokes the a2x program passed in the environment variable A2X
to create a minimal manual page. If A2X is set correctly, failing
this test is a good indicator that the docbook DTD or the
docbook XSL stylesheets are missing.
For adding further configure options about embedding DTLS support into
libcoap creating two new m4 functions AX_CHECK_GNUTLS_VERSION and
AX_CHECK_OPENSSL_VERSION.
The purpose of this new m4 functions is simply to check for the required
version of the combined library with a little bit of error handling.
As those checks are needed more than once later it's better to collect the
the logic and calls in dedicated m4 functions.
clang has dropped support for this warning and therefore emits
warnings when it is used as a compiler flag.
configure now uses AX_CHECK_COMPILE_FLAG[0] to check for compiler support.
[0] http://www.gnu.org/software/autoconf-archive/ax_check_compile_flag.html
Because local m4 macros are located in the sub-directory m4, autogen.sh
must not remove that directory but only clean the libtool-generated files.
Olaf Bergmann