Add support for the VDSO

[GabrielRavier]

Blink currently lacks support for the VDSO, which results in a lack of compatibility with many binaries.

In particular, binaries using dietlibc and any syscall implemented in the VDSO (such as clock_gettime) always segfault on dietlibc, as their strategy for dealing with getauxval(AT_SYSINFO_EHDR) == NULL is:

  if (!__vdso) __vdso=(char*)0xffffffffff600000;

(this appears to be for compatibility with ancient versions of Linux, and by that I mean versions from like 2002 from before even 2.6)