This commit moves all of the libraries under a common directory called libs/. This most certainly break libcxx and uClibc++ for now.

Squashed commit of the following:

    libs/libxx:  Fix some confusing in naming.  If the directory is called libxx, then the library must be libxx.a (unless perhaps LIBCXX is selected).
    libs/:  Fix paths in moved library directories.
    libs:  Brute force move of libc, libnx, and libxx to libs.  Cannot yet build it in that configuration.

libs/libnx/nxcontext.h

@@ -0,0 +1,129 @@
+/****************************************************************************
+ * libs/libnx/nxcontext.h
+ *
+ *   Copyright (C) 2013 Gregory Nutt. All rights reserved.
+ *   Author: Gregory Nutt <gnutt@nuttx.org>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ * 3. Neither the name NuttX nor the names of its contributors may be
+ *    used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ ****************************************************************************/
+
+#ifndef _LIBNX_NXCONTEXT_H
+#define _LIBNX_NXCONTEXT_H
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <nuttx/config.h>
+
+#include <sys/types.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <limits.h>
+#include <semaphore.h>
+
+#include <nuttx/streams.h>
+
+/****************************************************************************
+ * Pre-processor Definitions
+ ****************************************************************************/
+
+/* The NuttX NX library an be build in two modes: (1) as a standard, C-library
+ * that can be used by normal, user-space applications, or (2) as a special,
+ * kernel-mode NX-library only used within the OS.  If NuttX is not being
+ * built as separated kernel- and user-space modules, then only the first
+ * mode is supported.
+ */
+
+#if (defined(CONFIG_BUILD_PROTECTED) && defined(__KERNEL__)) || \
+     defined(CONFIG_BUILD_KERNEL)
+
+#  include <nuttx/kmalloc.h>
+
+   /* Domain-specific allocations */
+
+#  define lib_malloc(s)     kmm_malloc(s)
+#  define lib_zalloc(s)     kmm_zalloc(s)
+#  define lib_realloc(p,s)  kmm_realloc(p,s)
+#  define lib_memalign(p,s) kmm_memalign(p,s)
+#  define lib_free(p)       kmm_free(p)
+
+   /* User-accessible allocations */
+
+#  define lib_umalloc(s)    kumm_malloc(s)
+#  define lib_uzalloc(s)    kumm_zalloc(s)
+#  define lib_urealloc(p,s) kumm_realloc(p,s)
+#  define lib_ufree(p)      kumm_free(p)
+
+#else
+#  include <stdlib.h>
+
+   /* Domain-specific allocations */
+
+#  define lib_malloc(s)     malloc(s)
+#  define lib_zalloc(s)     zalloc(s)
+#  define lib_realloc(p,s)  realloc(p,s)
+#  define lib_free(p)       free(p)
+
+   /* User-accessible allocations */
+
+#  define lib_umalloc(s)    malloc(s)
+#  define lib_uzalloc(s)    zalloc(s)
+#  define lib_urealloc(p,s) realloc(p,s)
+#  define lib_ufree(p)      free(p)
+
+#endif
+
+/****************************************************************************
+ * Public Types
+ ****************************************************************************/
+
+/****************************************************************************
+ * Public Data
+ ****************************************************************************/
+
+#undef EXTERN
+#if defined(__cplusplus)
+#define EXTERN extern "C"
+extern "C"
+{
+#else
+#define EXTERN extern
+#endif
+
+/****************************************************************************
+ * Public Function Prototypes
+ ****************************************************************************/
+
+#undef EXTERN
+#if defined(__cplusplus)
+}
+#endif
+
+#endif /* _LIBNX_NXCONTEXT_H */