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
Merge branch 'master' into native-exec-bind-now