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/freopen.c

@@ -59,6 +59,8 @@ freopen(const char *file, const char *mode, FILE *fp)
 	if (!__sdidinit)
 		__sinit();
 
+	FLOCKFILE(fp);
+
 	/*
 	 * There are actually programs that depend on being able to "freopen"
 	 * descriptors that weren't originally open.  Keep this from breaking.
@@ -120,6 +122,7 @@ freopen(const char *file, const char *mode, FILE *fp)
 
 	if (f < 0) {			/* did not get it after all */
 		fp->_flags = 0;		/* set it free */
+		FUNLOCKFILE(fp);
 		errno = sverrno;	/* restore in case _close clobbered */
 		return (NULL);
 	}
@@ -154,5 +157,6 @@ freopen(const char *file, const char *mode, FILE *fp)
 	 */
 	if (oflags & O_APPEND)
 		(void) __sseek((void *)fp, (fpos_t)0, SEEK_END);
+	FUNLOCKFILE(fp);
 	return (fp);
 }