Create local C library implementation (2/2)

- This change is split into two separate patches in order to
  simplify the history as interpreted by 'git'. The split is
  between the move/rename and addition of new files.
- Remove dependency on toolchain C library headers and functions in
  order to ensure behavioural compatibility between toolchains.
- Use FreeBSD as reference for C library implementation.
- Do not let GCC use default library include paths.
- Remove unused definitions in modified headers and implementations.
- Move C library files to 'lib/stdlib' and 'include/stdlib'.
- Break std.c functions out into separate files.

Change-Id: I3e3d8d992052264d2a02489034ae4c03bf0f5512
diff --git a/include/stdlib/assert.h b/include/stdlib/assert.h
new file mode 100644
index 0000000..5621f8c
--- /dev/null
+++ b/include/stdlib/assert.h
@@ -0,0 +1,63 @@
+/*-
+ * Copyright (c) 1992, 1993
+ *	The Regents of the University of California.  All rights reserved.
+ * (c) UNIX System Laboratories, Inc.
+ * All or some portions of this file are derived from material licensed
+ * to the University of California by American Telephone and Telegraph
+ * Co. or Unix System Laboratories, Inc. and are reproduced herein with
+ * the permission of UNIX System Laboratories, Inc.
+ *
+ * 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 of the University 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 REGENTS 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 REGENTS 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.
+ *
+ *	@(#)assert.h	8.2 (Berkeley) 1/21/94
+ * $FreeBSD$
+ */
+
+#include <sys/cdefs.h>
+
+/*
+ * Unlike other ANSI header files, <assert.h> may usefully be included
+ * multiple times, with and without NDEBUG defined.
+ */
+
+#undef assert
+#undef _assert
+
+#ifdef NDEBUG
+#define	assert(e)	((void)0)
+#define	_assert(e)	((void)0)
+#else
+#define	_assert(e)	assert(e)
+
+#define	assert(e)	((e) ? (void)0 : __assert(__func__, __FILE__, \
+			    __LINE__, #e))
+#endif /* NDEBUG */
+
+#ifndef _ASSERT_H_
+#define _ASSERT_H_
+__BEGIN_DECLS
+void __assert(const char *, const char *, int, const char *) __dead2;
+__END_DECLS
+#endif /* !_ASSERT_H_ */