Consider the ELF e_entry point to be a gateway

For non-static ELFs, the loader clears the stack after doing its initialization
and jumps indirectly to the exe's e_entry function, which is usually _start
from crt0.o.  There is no retaddr on the stack, so _start can never return.
Therefore we can just go native directly without putting a return address on
the stack.

Review URL: https://codereview.appspot.com/7344043

git-svn-id: https://dynamorio.googlecode.com/svn/trunk@1910 49cc7528-f6fd-11dd-9d1a-b59b2e1864b6
native_exec: handle eagerly resolved ELF modules

If DT_BIND_NOW or its equivalents are set, then the resolver will be
NULL and the module fully relocated.  We don't need to replace it, and
we can't use it to check if we've already hooked the module or not.

Review URL: https://codereview.appspot.com/7328045

git-svn-id: https://dynamorio.googlecode.com/svn/trunk@1911 49cc7528-f6fd-11dd-9d1a-b59b2e1864b6