[libc] Add dlinfo + RTLD_DI_* macros to dlfcn.h (#149938)
An initial commit for #149911, this adds a stub implementation for
dlinfo and the enums list of `RTLD_DI_*` values.
While the dlinfo implementation relies on dynamic linker support, this
patch will add its prototype in the generated dlfcn.h header so that it
can be used by downstream platforms that have their own dlinfo
implementation.
