Add platform.h

Platform.h is intended to contain definitions and workarounds
for concepts that depend upon the used compiler and/or platform.

Currently it ensures that /thread_local/ is available irrespective
of whether the source is compiled in pre- or post C11 or C++11 mode.

This file should be included first by all MaxScale headers.

server/include/platform.h

@@ -0,0 +1,56 @@
+#ifndef _PLATFORM_H
+#define _PLATFORM_H
+/*
+ * This file is distributed as part of the MariaDB Corporation MaxScale.  It is free
+ * software: you can redistribute it and/or modify it under the terms of the
+ * GNU General Public License as published by the Free Software Foundation,
+ * version 2.
+ *
+ * This program 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 General Public License for more
+ * details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program; if not, write to the Free Software Foundation, Inc., 51
+ * Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Copyright MariaDB Corporation Ab 2016
+ */
+
+#if !defined(__cplusplus)
+
+#if __STDC_VERSION__ >= 201112
+
+#if defined(__STDC_NO_THREADS__)
+#define thread_local _Thread_local
+#else
+#include <threads.h>
+#endif
+
+#else // __STDC_VERSION >= 201112
+
+#if defined(__GNUC__)
+#define thread_local __thread
+#else
+#error Do not know how to define thread_local on this compiler/OS platform.
+#endif
+
+#endif
+
+#else // __cplusplus
+
+// C++11 supports thread_local natively.
+#if __cplusplus < 201103
+
+#if defined(__GNUC__)
+#define thread_local __thread
+#else
+#error Do not know how to define thread_local on this compiler/OS platform.
+#endif
+
+#endif // __cplusplus < 201103
+
+#endif // __cplusplus
+
+#endif // _PLATFORM_H