StdLib: Add support for AArch64

- Use some files from ARM version.
- Use NetBSD software floating point library to provide floating point
  operations not handled directly by hardware floating point enabled
  GCC compiler.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Harry Liebel <Harry.Liebel@arm.com>
Reviewed-by: Olivier Martin <Olivier.Martin@arm.com>
Reviewed-by: Daryl McDaniel <edk2-lists@mc2research.org>

git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@18118 6f19259b-4bc3-4df7-8a09-765794883524

StdLib/Include/Aarch64/machine/signal.h

@@ -0,0 +1,22 @@
+/**
+Copyright (c) 2010, Intel Corporation. All rights reserved.<BR>
+This program and the accompanying materials are licensed and made available under
+the terms and conditions of the BSD License that accompanies this distribution.
+The full text of the license may be found at
+http://opensource.org/licenses/bsd-license.php.
+
+THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
+WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
+
+**/
+#ifndef _MACHINE_SIGNAL_H
+#define _MACHINE_SIGNAL_H
+#include  <sys/EfiCdefs.h>
+
+/** The type sig_atomic_t is the (possibly volatile-qualified) integer type of
+    an object that can be accessed as an atomic entity, even in the presence
+    of asynchronous interrupts.
+**/
+typedef INTN sig_atomic_t;
+
+#endif    /* _MACHINE_SIGNAL_H */