license: add missing license headers

Some of the files in the Arduino core were missing the license headers.

They contain code which is either copied from previous Arduino cores
(which were already LGPL-2.1-or-later), or has been submitted to this
repository where most of the code is clearly LGPL-2.1-or-later.  In any
case, all the contributors have either been directly employed by Arduino
or have signed the CLA.

Add the missing LGPL-2.1-or-later headers to the files.

Author: pillo79

api/Common.cpp

@@ -1,3 +1,22 @@
+/*
+  Common.cpp - Common function implementations
+  Copyright (c) 2017 Arduino LLC. All right reserved.
+
+  This library is free software; you can redistribute it and/or
+  modify it under the terms of the GNU Lesser General Public
+  License as published by the Free Software Foundation; either
+  version 2.1 of the License, or (at your option) any later version.
+
+  This library is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public
+  License along with this library; if not, write to the Free Software
+  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
+*/
+
 #include "Common.h"
 
 /* C++ prototypes */

api/Common.h

@@ -1,3 +1,22 @@
+/*
+  Common.h - Common definitions for Arduino core
+  Copyright (c) 2017 Arduino LLC. All right reserved.
+
+  This library is free software; you can redistribute it and/or
+  modify it under the terms of the GNU Lesser General Public
+  License as published by the Free Software Foundation; either
+  version 2.1 of the License, or (at your option) any later version.
+
+  This library is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public
+  License along with this library; if not, write to the Free Software
+  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
+*/
+
 #pragma once
 #include <stdint.h>
 #include <stdbool.h>

api/Compat.h

@@ -1,3 +1,22 @@
+/*
+  Compat.h - Compatibility layer for Arduino API
+  Copyright (c) 2018 Arduino LLC. All right reserved.
+
+  This library is free software; you can redistribute it and/or
+  modify it under the terms of the GNU Lesser General Public
+  License as published by the Free Software Foundation; either
+  version 2.1 of the License, or (at your option) any later version.
+
+  This library is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public
+  License along with this library; if not, write to the Free Software
+  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
+*/
+
 #ifndef __COMPAT_H__
 #define __COMPAT_H__
 

api/Interrupts.h

@@ -1,3 +1,22 @@
+/*
+  Interrupts.h - Arduino interrupt management functions
+  Copyright (c) 2018 Arduino LLC. All right reserved.
+
+  This library is free software; you can redistribute it and/or
+  modify it under the terms of the GNU Lesser General Public
+  License as published by the Free Software Foundation; either
+  version 2.1 of the License, or (at your option) any later version.
+
+  This library is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public
+  License along with this library; if not, write to the Free Software
+  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
+*/
+
 #ifndef W_INTERRUPTS_CPP
 #define W_INTERRUPTS_CPP
 #ifdef __cplusplus