cmake HAVE_TALLOC_TEVENT examples

sahlberg/libnfs cmake/ConfigureChecks.cmake :53

check_c_source_compiles("#include <talloc.h>
                         #include <tevent.h>
                         int main(void)
                         {
                           struct tevent_context *ctx = tevent_context_init(NULL);
                           int major = talloc_version_major();
                         }"
                        HAVE_TALLOC_TEVENT)