When running autoconf-2.69 in here, we get:
configure.ac:57: 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.m4:2503: _AC_PREPROC_IFELSE is expanded from...
../../lib/autoconf/general.m4:2518: AC_PREPROC_IFELSE is expanded from...
configure.ac:57: the top level
configure.ac:61: 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.m4:2503: _AC_PREPROC_IFELSE is expanded from...
../../lib/autoconf/general.m4:2518: AC_PREPROC_IFELSE is expanded from...
configure.ac:61: the top level
Add AC_LANG_PROGRAM wrappings to fix these.