Rename maxscale/cpp.hh to maxscale/cppdefs.hh

Just like every c-header must include maxscale/cdefs.h as the first
file, every C++-header must include maxscale/cppdefs.hh as its first
header.

include/maxscale/cppdefs.hh

@@ -0,0 +1,65 @@
+#pragma once
+/*
+ * Copyright (c) 2016 MariaDB Corporation Ab
+ *
+ * Use of this software is governed by the Business Source License included
+ * in the LICENSE.TXT file and at www.mariadb.com/bsl.
+ *
+ * Change Date: 2019-07-01
+ *
+ * On the date above, in accordance with the Business Source License, use
+ * of this software will be governed by version 2 or later of the General
+ * Public License.
+ */
+
+/**
+ * @file cppdefs.hh
+ *
+ * This file is to be included first by all C++ headers.
+ */
+
+#if !defined(__cplusplus)
+#error This file is only to be included by C++ code.
+#endif
+
+#include <maxscale/cdefs.h>
+#include <exception>
+#include <new>
+#include <maxscale/log_manager.h>
+
+/**
+ * All classes of MaxScale are defined in the namespace @c maxscale.
+ *
+ * Third party plugins should not place any definitions inside the namespace
+ * to avoid any name clashes in the future. An exception are template
+ * specializations.
+ */
+namespace maxscale
+{
+}
+
+/**
+ * Shorthand for the @c maxscale namespace.
+ */
+namespace mxs = maxscale;
+
+/**
+ * If a statement is placed inside this macro, then no exceptions will
+ * escape. Typical use-case is for preventing exceptions to escape across
+ * a C-API.
+ *
+ * @code{.cpp}
+ *
+ *   void* cAPI()
+ *   {
+ *       void* rv = NULL;
+ *       MXS_EXCEPTION_GUARD(rv = new Something);
+ *       return rv;
+ *   }
+ * @endcode
+ */
+#define MXS_EXCEPTION_GUARD(statement)\
+    do { try { statement; }\
+    catch (const std::bad_alloc&) { MXS_OOM(); }\
+    catch (const std::exception& x) { MXS_ERROR("Caught standard exception: %s", x.what()); }\
+    catch (...) { MXS_ERROR("Caught unknown exception."); } } while (false)