Add SPDX license identifier if not present already in source file

Fixes: #9220

libsolidity/ast/AST.cpp

@@ -14,6 +14,7 @@
 	You should have received a copy of the GNU General Public License
 	along with solidity.  If not, see <http://www.gnu.org/licenses/>.
 */
+// SPDX-License-Identifier: GPL-3.0
 /**
  * @author Christian <c@ethdev.com>
  * @date 2014

libsolidity/ast/AST.h

@@ -14,6 +14,7 @@
 	You should have received a copy of the GNU General Public License
 	along with solidity.  If not, see <http://www.gnu.org/licenses/>.
 */
+// SPDX-License-Identifier: GPL-3.0
 /**
  * @author Christian <c@ethdev.com>
  * @date 2014

libsolidity/ast/ASTAnnotations.cpp

@@ -14,6 +14,7 @@
 	You should have received a copy of the GNU General Public License
 	along with solidity.  If not, see <http://www.gnu.org/licenses/>.
 */
+// SPDX-License-Identifier: GPL-3.0
 /**
  * @author Christian <c@ethdev.com>
  * @date 2015

libsolidity/ast/ASTAnnotations.h

@@ -14,6 +14,7 @@
 	You should have received a copy of the GNU General Public License
 	along with solidity.  If not, see <http://www.gnu.org/licenses/>.
 */
+// SPDX-License-Identifier: GPL-3.0
 /**
  * @author Christian <c@ethdev.com>
  * @date 2015

libsolidity/ast/ASTEnums.h

@@ -14,6 +14,7 @@
 	You should have received a copy of the GNU General Public License
 	along with solidity.  If not, see <http://www.gnu.org/licenses/>.
 */
+// SPDX-License-Identifier: GPL-3.0
 /**
  * @date 2017
  * Enums for AST classes.

libsolidity/ast/ASTForward.h

@@ -14,6 +14,7 @@
 	You should have received a copy of the GNU General Public License
 	along with solidity.  If not, see <http://www.gnu.org/licenses/>.
 */
+// SPDX-License-Identifier: GPL-3.0
 /**
  * @author Christian <c@ethdev.com>
  * @date 2014

libsolidity/ast/ASTJsonConverter.cpp

@@ -14,6 +14,7 @@
 	You should have received a copy of the GNU General Public License
 	along with solidity.  If not, see <http://www.gnu.org/licenses/>.
 */
+// SPDX-License-Identifier: GPL-3.0
 /**
  * @date 2017
  * Converts the AST into json format

libsolidity/ast/ASTJsonConverter.h

@@ -14,6 +14,7 @@
 	You should have received a copy of the GNU General Public License
 	along with solidity.  If not, see <http://www.gnu.org/licenses/>.
 */
+// SPDX-License-Identifier: GPL-3.0
 /**
  * @author Lefteris <lefteris@ethdev.com>
  * @date 2015

libsolidity/ast/ASTJsonImporter.cpp

@@ -14,6 +14,7 @@
 	You should have received a copy of the GNU General Public License
 	along with solidity.  If not, see <http://www.gnu.org/licenses/>.
 */
+// SPDX-License-Identifier: GPL-3.0
 /**
  * @author julius <djudju@protonmail.com>
  * @date 2019

libsolidity/ast/ASTJsonImporter.h

@@ -14,6 +14,7 @@
 	You should have received a copy of the GNU General Public License
 	along with solidity.  If not, see <http://www.gnu.org/licenses/>.
 */
+// SPDX-License-Identifier: GPL-3.0
 /**
  * @author julius <djudju@protonmail.com>
  * @date 2019

libsolidity/ast/ASTUtils.cpp

@@ -14,6 +14,7 @@
 	You should have received a copy of the GNU General Public License
 	along with solidity.  If not, see <http://www.gnu.org/licenses/>.
 */
+// SPDX-License-Identifier: GPL-3.0
 
 #include <libsolidity/ast/AST.h>
 #include <libsolidity/ast/ASTUtils.h>

libsolidity/ast/ASTUtils.h

@@ -14,6 +14,7 @@
 	You should have received a copy of the GNU General Public License
 	along with solidity.  If not, see <http://www.gnu.org/licenses/>.
 */
+// SPDX-License-Identifier: GPL-3.0
 
 #pragma once
 

libsolidity/ast/ASTVisitor.h

@@ -14,6 +14,7 @@
 	You should have received a copy of the GNU General Public License
 	along with solidity.  If not, see <http://www.gnu.org/licenses/>.
 */
+// SPDX-License-Identifier: GPL-3.0
 /**
  * @author Christian <c@ethdev.com>
  * @date 2014

libsolidity/ast/AST_accept.h

@@ -14,6 +14,7 @@
 	You should have received a copy of the GNU General Public License
 	along with solidity.  If not, see <http://www.gnu.org/licenses/>.
 */
+// SPDX-License-Identifier: GPL-3.0
 /**
  * @author Christian <c@ethdev.com>
  * @date 2014

libsolidity/ast/AsmJsonImporter.cpp

@@ -14,6 +14,7 @@
 	You should have received a copy of the GNU General Public License
 	along with solidity.  If not, see <http://www.gnu.org/licenses/>.
 */
+// SPDX-License-Identifier: GPL-3.0
 /**
  * @author julius <djudju@protonmail.com>
  * @date 2019

libsolidity/ast/AsmJsonImporter.h

@@ -14,6 +14,7 @@
 	You should have received a copy of the GNU General Public License
 	along with solidity.  If not, see <http://www.gnu.org/licenses/>.
 */
+// SPDX-License-Identifier: GPL-3.0
 /**
  * @author julius <djudju@protonmail.com>
  * @date 2019

libsolidity/ast/ExperimentalFeatures.h

@@ -14,6 +14,7 @@
 	You should have received a copy of the GNU General Public License
 	along with solidity.  If not, see <http://www.gnu.org/licenses/>.
 */
+// SPDX-License-Identifier: GPL-3.0
 /**
  * List of experimental features.
  */

libsolidity/ast/TypeProvider.cpp

@@ -14,6 +14,7 @@
 	You should have received a copy of the GNU General Public License
 	along with solidity.  If not, see <http://www.gnu.org/licenses/>.
 */
+// SPDX-License-Identifier: GPL-3.0
 
 #include <libsolidity/ast/AST.h>
 #include <libsolidity/ast/TypeProvider.h>

libsolidity/ast/TypeProvider.h

@@ -14,6 +14,7 @@
 	You should have received a copy of the GNU General Public License
 	along with solidity.  If not, see <http://www.gnu.org/licenses/>.
 */
+// SPDX-License-Identifier: GPL-3.0
 
 #pragma once
 

libsolidity/ast/Types.cpp

@@ -14,6 +14,7 @@
 	You should have received a copy of the GNU General Public License
 	along with solidity.  If not, see <http://www.gnu.org/licenses/>.
 */
+// SPDX-License-Identifier: GPL-3.0
 /**
  * @author Christian <c@ethdev.com>
  * @date 2014

libsolidity/ast/Types.h

@@ -14,6 +14,7 @@
 	You should have received a copy of the GNU General Public License
 	along with solidity.  If not, see <http://www.gnu.org/licenses/>.
 */
+// SPDX-License-Identifier: GPL-3.0
 /**
  * @author Christian <c@ethdev.com>
  * @date 2014