[Feature Request] dlopen_from function

[Jakob Skaar <jakobrs100@gmail.com>]

Hi,

The behaviour of certain functions in libdl[^2] like the `dlopen`
function is dependent on where it is called from. This is normally
what you want, but sometimes you may want to specify the caller
address yourself, for example when intercepting/hooking the `dlopen`
function itself. For this reason, Apple has added the `dlopen_from`
function in macOS Big Sur. `dlopen_from` has an extra parameter, `void
*caller`, that specifies the "fake" caller address to be used instead
of `RETURN_ADDRESS(0)`[^3]. Using `dlopen_from` significantly
simplifies intercepting `dlopen` calls (see [here][1] for an example).
So my feature request is to implement `dlopen_from` in glibc too.

[1]: <https://github.com/clementgallet/libTAS/blob/70966f9e1f400dfdd5176bba63c11cb6026d3da6/src/library/dlhook.cpp#L108-L189>
[^2]: The same logic also applies to `dlmopen`, `dlsym`, and `dlvsym`.
[^3]: Header file where `dlopen_from` is declared:
<https://opensource.apple.com/source/dyld/dyld-832.7.3/include/dlfcn_private.h.auto.html>