RFR: 8282306: os::is_first_C_frame(frame*) crashes on invalid link access [v10]

[Johannes Bechberger]

> This PR introduces a new method `can_access_link` into the frame class to check the accessibility of the link information. It furthermore adds a new `os::is_first_C_frame(frame*, Thread*)` that uses the `can_access_link` method
> and the passed thread object to check the validity of frame pointer, stack pointer, sender frame pointer and sender stack pointer. This should reduce the possibilities for crashes.

Johannes Bechberger has updated the pull request incrementally with one additional commit since the last revision:

  Fix problem related to NMT
  
  The problem is that registering a thread for NMT uses
  the os::is_first_C_frame method which calls Thread::enable_wx
  internally. But enable_wx requires that the init_wx method
  has been called before, not after.
  Swapping two lines therefore fixes the problem.

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/7591/files
  - new: https://git.openjdk.java.net/jdk/pull/7591/files/1f08203f..1714b69a

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=7591&range=09
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=7591&range=08-09

  Stats: 4 lines in 1 file changed: 2 ins; 2 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7591.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7591/head:pull/7591

PR: https://git.openjdk.java.net/jdk/pull/7591