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/libc/stdio/lib_libfflush.c

@@ -0,0 +1,187 @@
+/****************************************************************************
+ * libs/libc/stdio/lib_libfflush.c
+ *
+ *   Copyright (C) 2007-2008, 2011-2014, 2017 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.
+ *
+ ****************************************************************************/
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <nuttx/config.h>
+
+#include <sys/types.h>
+#include <stdbool.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <errno.h>
+
+#include <nuttx/fs/fs.h>
+
+#include "libc.h"
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: lib_fflush
+ *
+ * Description:
+ *  The function lib_fflush() forces a write of all user-space buffered data for
+ *  the given output or update stream via the stream's underlying write
+ *  function.  The open status of the stream is unaffected.
+ *
+ * Input Parameters:
+ *  stream - the stream to flush
+ *  bforce - flush must be complete.
+ *
+ * Returned Value:
+ *  A negated errno value on failure, otherwise the number of bytes remaining
+ *  in the buffer.
+ *
+ ****************************************************************************/
+
+ssize_t lib_fflush(FAR FILE *stream, bool bforce)
+{
+#ifndef CONFIG_STDIO_DISABLE_BUFFERING
+  FAR const unsigned char *src;
+  ssize_t bytes_written;
+  ssize_t nbuffer;
+  int ret;
+
+  /* Return EBADF if the file is not opened for writing */
+
+  if (stream->fs_fd < 0 || (stream->fs_oflags & O_WROK) == 0)
+    {
+      return -EBADF;
+    }
+
+  /* Make sure that we have exclusive access to the stream */
+
+  lib_take_semaphore(stream);
+
+  /* Check if there is an allocated I/O buffer */
+
+  if (stream->fs_bufstart == NULL)
+    {
+      /* No, then there can be nothing remaining in the buffer. */
+
+      ret = 0;
+      goto errout_with_sem;
+   }
+
+  /* Make sure that the buffer holds valid data */
+
+  if (stream->fs_bufpos != stream->fs_bufstart)
+    {
+      /* Make sure that the buffer holds buffered write data.  We do not
+       * support concurrent read/write buffer usage.
+       */
+
+      if (stream->fs_bufread != stream->fs_bufstart)
+        {
+          /* The buffer holds read data... just return zero meaning "no bytes
+           * remaining in the buffer."
+           */
+
+          ret = 0;
+          goto errout_with_sem;
+        }
+
+      /* How many bytes of write data are used in the buffer now */
+
+      nbuffer = stream->fs_bufpos - stream->fs_bufstart;
+
+      /* Try to write that amount */
+
+      src = stream->fs_bufstart;
+      do
+        {
+          /* Perform the write */
+
+          bytes_written = _NX_WRITE(stream->fs_fd, src, nbuffer);
+          if (bytes_written < 0)
+            {
+              /* Write failed.  The cause of the failure is in 'errno'.
+               * returned the negated errno value.
+               */
+
+              stream->fs_flags |= __FS_FLAG_ERROR;
+              ret = _NX_GETERRVAL(bytes_written);
+              goto errout_with_sem;
+            }
+
+          /* Handle partial writes.  fflush() must either return with
+           * an error condition or with the data successfully flushed
+           * from the buffer.
+           */
+
+          src     += bytes_written;
+          nbuffer -= bytes_written;
+        }
+      while (bforce && nbuffer > 0);
+
+      /* Reset the buffer position to the beginning of the buffer */
+
+      stream->fs_bufpos = stream->fs_bufstart;
+
+      /* For the case of an incomplete write, nbuffer will be non-zero
+       * It will hold the number of bytes that were not written.
+       * Move the data down in the buffer to handle this (rare) case
+       */
+
+      while (nbuffer)
+       {
+         *stream->fs_bufpos++ = *src++;
+         --nbuffer;
+       }
+    }
+
+  /* Restore normal access to the stream and return the number of bytes
+   * remaining in the buffer.
+   */
+
+  lib_give_semaphore(stream);
+  return stream->fs_bufpos - stream->fs_bufstart;
+
+errout_with_sem:
+  lib_give_semaphore(stream);
+  return ret;
+
+#else
+  /* Return no bytes remaining in the buffer */
+
+  return 0;
+#endif
+}
+