Use `dlsym` to resolve `__vdso_clock_gettime` etc.?

In dynamically linked executables, we should be able to `dlopen` the "linux-vdso.so" library and use `dlsym` to obtain symbols like "__vdso_clock_gettime" instead of parsing the vDSO ELF image manually.

An alternative would be to say that since a dynamically-linked executable has libc anyway, the time routines should just use the libc `clock_gettime` APIs.