cmake HAVE_LIBCURL_766 examples

Unidata/netcdf-c cmake/dependencies.cmake :271

CHECK_C_SOURCE_COMPILES("
  #include <curl/curl.h>
  int main() {
  #if LIBCURL_VERSION_NUM < 0x074200
        choke me;
  #endif
  }" HAVE_LIBCURL_766)