[tsan] Fix ScopedInterceptor's handling of !thr->is_inited

[kubamracek]

Summary

The commit r257866 (https://github.com/llvm-mirror/compiler-rt/commit/b78f9c1f623e5faa4cca68227ab536ae80f9fc16, differential revision http://reviews.llvm.org/D15301, which is slightly different than the commit) introduced a test failure in Darwin/ignored-interceptors.mm. When ignore_interceptors_accesses=1, we only check !thr_->is_inited in the constructor of ScopedInterceptor, which then skips ThreadIgnoreBegin, but the destructor still calls ThreadIgnoreEnd:

ScopedInterceptor::ScopedInterceptor(...) {
  Initialize(thr);
  if (!thr_->is_inited)
    return;
  ...
  if (flags()->ignore_interceptors_accesses) ThreadIgnoreBegin(thr_, pc_);
}
ScopedInterceptor::~ScopedInterceptor() {
  if (flags()->ignore_interceptors_accesses) ThreadIgnoreEnd(thr_, pc_);
  ...
}

[yabinc]

Sorry, I missed two lines when committing http://reviews.llvm.org/D15301. I uploaded the fix in http://reviews.llvm.org/D15301.
I think if !thr->is_inited, it means __tsan_thread_start_func()->ThreadStart() is not called, and I think we shouldn't access
fields in ThreadState as it is not inited. Please let me know if my understanding is wrong.

lib/tsan/rtl/tsan_interceptors.cc

 #endif
 
 ScopedInterceptor::ScopedInterceptor(ThreadState *thr, const char *fname,
                                      uptr pc)
     : thr_(thr)
     , pc_(pc)
     , in_ignored_lib_(false) {
   Initialize(thr);
-  if (!thr_->is_inited)
-    return;
-  if (!thr_->ignore_interceptors)
+  if (thr_->is_inited && !thr_->ignore_interceptors)
     FuncEntry(thr, pc);
   DPrintf("#%d: intercept %s()\n", thr_->tid, fname);
   if (!thr_->in_ignored_lib && libignore()->IsIgnored(pc)) {
     in_ignored_lib_ = true;
     thr_->in_ignored_lib = true;
     ThreadIgnoreBegin(thr_, pc_);
   }
   if (flags()->ignore_interceptors_accesses) ThreadIgnoreBegin(thr_, pc_);