Remove historical workarounds.

We removed libcorkscrew in L, and we removed its replacement in P.

We removed the LLVM uses several years ago too.

Bug: N/A
Test: builds
Change-Id: I414c9c3dc3c2c2e0016b9da0e9f8aa16068daa8c
diff --git a/runtime/runtime.cc b/runtime/runtime.cc
index 4068158..f550a15 100644
--- a/runtime/runtime.cc
+++ b/runtime/runtime.cc
@@ -575,19 +575,7 @@
     LOG(FATAL_WITHOUT_ABORT) << "Unexpectedly returned from abort hook!";
   }
 
-#if defined(__GLIBC__)
-  // TODO: we ought to be able to use pthread_kill(3) here (or abort(3),
-  // which POSIX defines in terms of raise(3), which POSIX defines in terms
-  // of pthread_kill(3)). On Linux, though, libcorkscrew can't unwind through
-  // libpthread, which means the stacks we dump would be useless. Calling
-  // tgkill(2) directly avoids that.
-  syscall(__NR_tgkill, getpid(), GetTid(), SIGABRT);
-  // TODO: LLVM installs it's own SIGABRT handler so exit to be safe... Can we disable that in LLVM?
-  // If not, we could use sigaction(3) before calling tgkill(2) and lose this call to exit(3).
-  exit(1);
-#else
   abort();
-#endif
   // notreached
 }