x86: compile everything with relro / bind_now

Enable relro / bind_now when compiling Android applications.
This marks certain regions of memory as read-only after linking,
making memory corruption security vulnerabilities are harder
to exploit.

See:
 * http://www.akkadia.org/drepper/nonselsec.pdf (section 6)
 * http://tk-blog.blogspot.com/2009/02/relro-not-so-well-known-memory.html

relro support has been enabled for ARM since 233d460f.
This change enables it for x86.

Change-Id: Ib90704f2fecffcfdc3587607112804faa0e16385