No (un)setenv until SUSv3 (e.g. Solaris 2.9). (fallback untested)
AC_CHECK_FUNCS(snprintf _snprintf )
AC_CHECK_FUNCS(popen _popen )
AC_CHECK_FUNCS(pclose _pclose )
+AC_CHECK_FUNCS(setenv unsetenv)
dnl ** check for specific library functions that we are interested in
/* Define if you have the `popen' function. */
#undef HAVE_POPEN
+/* Define if you have the `setenv' function. */
+#undef HAVE_SETENV
+
+/* Define if you have the `unsetenv' function. */
+#undef HAVE_UNSETENV
+
/* Define if you have the <pthread.h> header file. */
#undef HAVE_PTHREAD_H