Replace stdatomic.h (C11 standard compliant header) by a custom one

to increase C++ compatibility as stdatomic.h doesn't work in C++!

(I would like to thanks the one(s) who thought it was a good idea
***not*** to include stdatomic.h -and thread.h- in the C++ standard!)

m-atomic.h

@@ -0,0 +1,95 @@
+/*
+ * M*LIB - Thin stdatomic wrapper for C++ compatibility
+ *
+ * Copyright (c) 2017, Patrick Pelissier
+ * All rights reserved.
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ * + Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ * + Redistributions in binary form must reproduce the above copyright
+ *   notice, this list of conditions and the following disclaimer in the
+ *   documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE REGENTS AND CONTRIBUTORS BE LIABLE FOR ANY
+ * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+*/
+#ifndef __M_ATOMIC_H
+#define __M_ATOMIC_H
+
+/* NOTE: Due to the C++ not having recognized stdatomic.h officialy,
+   it is hard to use this header directly with a C++ compiler like 
+   g++ or MSVC.
+   (See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60932 ).
+   clang has no issue with this header.*/
+#if defined(__cplusplus) && __cplusplus >= 201103L && !defined(__clang__)
+
+/* NOTE: This is what the stdatomic.h header shall do in C++ mode. */
+#include <atomic>
+
+using std::memory_order;
+
+using std::atomic_bool;
+using std::atomic_char;
+using std::atomic_short;
+using std::atomic_int;
+using std::atomic_long;
+using std::atomic_llong;
+using std::atomic_uchar;
+using std::atomic_schar;
+using std::atomic_ushort;
+using std::atomic_uint;
+using std::atomic_ulong;
+using std::atomic_ullong;
+using std::atomic_intptr_t;
+using std::atomic_uintptr_t;
+using std::atomic_size_t;
+using std::atomic_ptrdiff_t;
+using std::atomic_intmax_t;
+using std::atomic_uintmax_t;
+using std::atomic_flag;
+
+using std::kill_dependency;
+using std::atomic_thread_fence;
+using std::atomic_signal_fence;
+using std::atomic_is_lock_free;
+using std::atomic_store_explicit;
+using std::atomic_store;
+using std::atomic_load_explicit;
+using std::atomic_load;
+using std::atomic_exchange_explicit;
+using std::atomic_exchange;
+using std::atomic_compare_exchange_strong_explicit;
+using std::atomic_compare_exchange_strong;
+using std::atomic_compare_exchange_weak_explicit;
+using std::atomic_compare_exchange_weak;
+using std::atomic_fetch_add;
+using std::atomic_fetch_add_explicit;
+using std::atomic_fetch_sub;
+using std::atomic_fetch_sub_explicit;
+using std::atomic_fetch_or;
+using std::atomic_fetch_or_explicit;
+using std::atomic_fetch_xor;
+using std::atomic_fetch_xor_explicit;
+using std::atomic_fetch_and;
+using std::atomic_fetch_and_explicit;
+using std::atomic_flag_test_and_set;
+using std::atomic_flag_test_and_set_explicit;
+using std::atomic_flag_clear;
+using std::atomic_flag_clear_explicit;
+
+#else
+
+#include <stdatomic.h>
+
+#endif
+
+#endif

m-i-shared.h

@@ -28,9 +28,9 @@
 #include <stdlib.h>
 #include <stdbool.h>
 #include <assert.h>
-#include <stdatomic.h>
 
 #include "m-core.h"
+#include "m-atomic.h"
 
 /* Define the oplist of a intrusive shared pointer.
    USAGE: ISHARED_OPLIST(name [, oplist_of_the_type]) */

m-shared.h

@@ -28,10 +28,10 @@
 #include <stdlib.h>
 #include <stdbool.h>
 #include <assert.h>
-#include <stdatomic.h>
 #include <stdint.h>
 
 #include "m-core.h"
+#include "m-atomic.h"
 
 /* Define the oplist of a shared pointer.
    USAGE: SHARED_OPLIST(name [, oplist_of_the_type]) */

m-snapshot.h

@@ -26,8 +26,8 @@
 #define __M_SNAPSHOT
 
 #include <assert.h>
-#include <stdatomic.h>
 
+#include "m-atomic.h"
 #include "m-core.h"
 
 /* Define a snapshot and it function