AC_LANG_PROGRAM needs to be quoted when used within AC_*_IFELSE:
https://lists.gnu.org/archive/html/bug-autoconf/2011-04/msg00017.html
This fixes the following warnings:
$ autoreconf
configure.ac:298: warning: AC_LANG_CONFTEST: no AC_LANG_SOURCE call detected in body
../../lib/autoconf/lang.m4:193: AC_LANG_CONFTEST is expanded from...
../../lib/autoconf/general.m4:2729: _AC_RUN_IFELSE is expanded from...
../../lib/m4sugar/m4sh.m4:639: AS_IF is expanded from...
../../lib/autoconf/general.m4:2748: AC_RUN_IFELSE is expanded from...
configure.ac:298: the top level
configure.ac:593: warning: AC_LANG_CONFTEST: no AC_LANG_SOURCE call detected in body
../../lib/autoconf/lang.m4:193: AC_LANG_CONFTEST is expanded from...
../../lib/autoconf/general.m4:2661: _AC_LINK_IFELSE is expanded from...
../../lib/autoconf/general.m4:2678: AC_LINK_IFELSE is expanded from...
configure.ac:593: the top level
...
configure.ac:309: warning: AC_LANG_CONFTEST: no AC_LANG_SOURCE call detected in body
../../lib/autoconf/lang.m4:193: AC_LANG_CONFTEST is expanded from...
../../lib/autoconf/general.m4:2729: _AC_RUN_IFELSE is expanded from...
../../lib/m4sugar/m4sh.m4:639: AS_IF is expanded from...
../../lib/autoconf/general.m4:2748: AC_RUN_IFELSE is expanded from...
configure.ac:309: the top level
...
This allows for some further hardening against synflooding and connection flooding
where no data is actually sent, as the kernel will simply ignore those connections
(well, as far as the ircd is concerned anyway).