Provide our own newlib libc

Newlib 2.2.0 w/ nan ofeatures, xtensa patches, locking
implementation.

Built from https://github.com/projectgus/newlib-xtensa
branch xtensa-2_2_0-lock
commit daa6ae40cdc8099f54c3e68a586fc1b906169c5a

For more details, see:
https://github.com/SuperHouse/esp-open-rtos/wiki/libc-configuration

Closes #1

libc/xtensa-lx106-elf/include/sys/lock.h

@@ -0,0 +1,50 @@
+#ifndef _XTENSA_LOCK_H__
+#define _XTENSA_LOCK_H__
+
+/* generic lock implementation.
+
+   Weak linked stub _lock functions in lock.c, can be
+   replaced with a lock implementation at link time.
+
+ */
+
+typedef int _lock_t;
+typedef _lock_t _LOCK_RECURSIVE_T;
+typedef _lock_t _LOCK_T;
+
+#include <_ansi.h>
+
+/* NOTE: some parts of newlib statically initialise locks via
+   __LOCK_INIT, some initialise at runtime via __lock_init. So need to
+   support possibility that a _lock_t is null during first call to
+   _lock_acquire or _lock_try_acquire.
+
+   Lock functions all take a pointer to the _lock_t entry, so the
+   value stored there can be manipulated.
+*/
+#define __LOCK_INIT(CLASS,NAME) CLASS _lock_t NAME = 0;
+#define __LOCK_INIT_RECURSIVE(CLASS,NAME) CLASS _lock_t NAME = 0;
+
+void _lock_init(_lock_t *lock);
+void _lock_init_recursive(_lock_t *lock);
+void _lock_close(_lock_t *lock);
+void _lock_close_recursive(_lock_t *lock);
+void _lock_acquire(_lock_t *lock);
+void _lock_acquire_recursive(_lock_t *lock);
+int _lock_try_acquire(_lock_t *lock);
+int _lock_try_acquire_recursive(_lock_t *lock);
+void _lock_release(_lock_t *lock);
+void _lock_release_recursive(_lock_t *lock);
+
+#define __lock_init(lock) _lock_init(&(lock))
+#define __lock_init_recursive(lock) _lock_init_recursive(&(lock))
+#define __lock_close(lock) _lock_close(&(lock))
+#define __lock_close_recursive(lock) _lock_close_recursive(&(lock))
+#define __lock_acquire(lock) _lock_acquire(&(lock))
+#define __lock_acquire_recursive(lock) _lock_acquire_recursive(&(lock))
+#define __lock_try_acquire(lock) _lock_try_acquire(&(lock))
+#define __lock_try_acquire_recursive(lock) _lock_try_acquire_recursive(&(lock))
+#define __lock_release(lock) _lock_release(&(lock))
+#define __lock_release_recursive(lock) _lock_release_recursive(&(lock))
+
+#endif /* _XTENSA_LOCK_H__ */