In C++, a function declaration with an empty parameter list means that
the function takes no arguments. In C, however, it means that the
function takes an unspecified number of parameters.
What we did previously was therefore non-conforming. This caused a
config check to fail in the curl port, as it was able to redeclare
`rand` as taking an int parameter.
This implements the dladdr() function which lets the caller look up
the symbol name, symbol address as well as library name and library
base address for an arbitrary address.
This implements more of the dlfcn functionality. Most notably:
* It's now possible to dlopen() libraries which were already
loaded at program startup time. This does not cause those
libraries to be loaded twice.
* Errors are reported via dlerror() rather than by crashing
the program.
* Calls to the dl*() functions are thread-safe.
