Add MIT license to build-aux/m4 scripts

Github-Pull: bitcoin#8784
Rebased-From: 0c4e6ce

build-aux/m4/bitcoin_find_bdb48.m4

@@ -1,3 +1,7 @@
+dnl Copyright (c) 2013-2015 The Bitcoin Core developers
+dnl Distributed under the MIT software license, see the accompanying
+dnl file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
 AC_DEFUN([BITCOIN_FIND_BDB48],[
   AC_MSG_CHECKING([for Berkeley DB C++ headers])
   BDB_CPPFLAGS=

build-aux/m4/bitcoin_qt.m4

@@ -1,3 +1,7 @@
+dnl Copyright (c) 2013-2016 The Bitcoin Core developers
+dnl Distributed under the MIT software license, see the accompanying
+dnl file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
 dnl Helper for cases where a qt dependency is not met.
 dnl Output: If qt version is auto, set bitcoin_enable_qt to false. Else, exit.
 AC_DEFUN([BITCOIN_QT_FAIL],[

build-aux/m4/bitcoin_subdir_to_include.m4

@@ -1,3 +1,7 @@
+dnl Copyright (c) 2013-2014 The Bitcoin Core developers
+dnl Distributed under the MIT software license, see the accompanying
+dnl file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
 dnl BITCOIN_SUBDIR_TO_INCLUDE([CPPFLAGS-VARIABLE-NAME],[SUBDIRECTORY-NAME],[HEADER-FILE])
 dnl SUBDIRECTORY-NAME must end with a path separator
 AC_DEFUN([BITCOIN_SUBDIR_TO_INCLUDE],[

build-aux/m4/l_atomic.m4

@@ -1,3 +1,9 @@
+dnl Copyright (c) 2015 Tim Kosse <tim.kosse@filezilla-project.org>
+dnl Copying and distribution of this file, with or without modification, are
+dnl permitted in any medium without royalty provided the copyright notice
+dnl and this notice are preserved. This file is offered as-is, without any
+dnl warranty.
+
 # Some versions of gcc/libstdc++ require linking with -latomic if
 # using the C++ atomic library.
 #