libc: speed-up flockfile()/funlockfile()

For Honeycomb, we added proper file thread-safety for
all FILE* operations. However, we did implement that by
using an out-of-band hash table to map FILE* pointers
to phtread_mutex_t mutexes, because we couldn't change
the size of 'struct _sFILE' without breaking the ABI.

It turns out that our BSD-derived code already has
some support code to extend FILE* objects, so use it
instead. See libc/stdio/fileext.h

This patch gets rid of the hash table, and put the
mutex directly into the sFILE extension.

Change-Id: If1c3fe0a0a89da49c568e9a7560b7827737ff4d0
diff --git a/libc/include/pthread.h b/libc/include/pthread.h
index 9d05769..2015ac0 100644
--- a/libc/include/pthread.h
+++ b/libc/include/pthread.h
@@ -42,9 +42,13 @@
     int volatile value;
 } pthread_mutex_t;
 
-#define  PTHREAD_MUTEX_INITIALIZER             {0}
-#define  PTHREAD_RECURSIVE_MUTEX_INITIALIZER   {0x4000}
-#define  PTHREAD_ERRORCHECK_MUTEX_INITIALIZER  {0x8000}
+#define  __PTHREAD_MUTEX_INIT_VALUE            0
+#define  __PTHREAD_RECURSIVE_MUTEX_INIT_VALUE  0x4000
+#define  __PTHREAD_ERRORCHECK_MUTEX_INIT_VALUE 0x8000
+
+#define  PTHREAD_MUTEX_INITIALIZER             {__PTHREAD_MUTEX_INIT_VALUE}
+#define  PTHREAD_RECURSIVE_MUTEX_INITIALIZER   {__PTHREAD_RECURSIVE_MUTEX_INIT_VALUE}
+#define  PTHREAD_ERRORCHECK_MUTEX_INITIALIZER  {__PTHREAD_ERRORCHECK_MUTEX_INIT_VALUE}
 
 enum {
     PTHREAD_MUTEX_NORMAL = 0,