Fix the handle locking in stdio

Fix the handle locking in stdio to use flockfile/funlockfile
internally when and where required.  Macros in <stdio.h> are updated
to automatically call the underlying functions when the process is
threaded to obtain the necessary locking.  A private mutex is added
to protect __sglue, the internal list of FILE handles, and another
to protect the one-time initialization.  Some routines in libc that
use getc() change to use getc_unlocked() as they're either protected
by their own lock or aren't thread-safe routines anyway.

Based on OpenBSD change by guenther@openbsd.org
http://www.mail-archive.com/source-changes@cvs.openbsd.org/msg01015.html

Bug: 3446659
Change-Id: Ie82116e358c541718d6709ec45ca6796be5a007b

libc/stdio/feof.c

@@ -32,6 +32,7 @@
  */
 
 #include <stdio.h>
+#include "local.h"
 
 /*
  * A subroutine version of the macro feof.
@@ -41,5 +42,10 @@
 int
 feof(FILE *fp)
 {
-	return (__sfeof(fp));
+	int ret;
+
+	FLOCKFILE(fp);
+	ret = __sfeof(fp);
+	FUNLOCKFILE(fp);
+	return (ret);
 }