Clean up abort.

* A dlmalloc usage error shouldn't call abort(3) because we want to
  cause a SIGSEGV by writing the address dlmalloc didn't like to an
  address the kernel won't like, so that debuggerd will dump the
  memory around the address that upset dlmalloc.

* Switch to the simpler FreeBSD/NetBSD style of registering stdio
  cleanup. Hopefully this will let us simplify more of the stdio
  implementation.

* Clear the stdio cleanup handler before we abort because of a dlmalloc
  corruption error. This fixes the reported bug, where we'd hang inside
  dlmalloc because the stdio cleanup reentered dlmalloc.

Bug: 9301265
Change-Id: Ief31b389455d6876e5a68f0f5429567d37277dbc
diff --git a/libc/stdio/setvbuf.c b/libc/stdio/setvbuf.c
index 2fb76af..eb0ec68 100644
--- a/libc/stdio/setvbuf.c
+++ b/libc/stdio/setvbuf.c
@@ -124,8 +124,7 @@
 		flags |= __SNPT;
 
 	/*
-	 * Fix up the FILE fields, and set __cleanup for output flush on
-	 * exit (since we are buffered in some way).
+	 * Fix up the FILE fields.
 	 */
 	if (mode == _IOLBF)
 		flags |= __SLBF;
@@ -148,7 +147,6 @@
 		fp->_w = 0;
 	}
 	FUNLOCKFILE(fp);
-	__atexit_register_cleanup(_cleanup);
 
 	return (ret);
 }