Include <atomic> for std::atomic where needed

Fixes build with Boost 1.75

atomic.patch

@@ -0,0 +1,25 @@
+From 19d28524e76ff9c5b7fa4ff1a8373bfbacad9775 Mon Sep 17 00:00:00 2001
+From: Yuri D'Elia <wavexx@thregr.org>
+Date: Sun, 13 Dec 2020 19:41:47 +0100
+Subject: [PATCH] Include <atomic> for std::atomic where needed
+
+Fixes build on linux using clang 11
+---
+ src/slic3r/GUI/Mouse3DController.hpp | 1 +
+ 1 file changed, 1 insertion(+)
+
+diff --git a/src/slic3r/GUI/Mouse3DController.hpp b/src/slic3r/GUI/Mouse3DController.hpp
+index eb1425b..4e0c8e6 100644
+--- a/src/slic3r/GUI/Mouse3DController.hpp
++++ b/src/slic3r/GUI/Mouse3DController.hpp
+@@ -8,6 +8,7 @@
+ 
+ #include "hidapi.h"
+ 
++#include <atomic>
+ #include <queue>
+ #include <thread>
+ #include <vector>
+-- 
+2.30.0
+

prusa-slicer.spec

@@ -31,6 +31,11 @@ Source2:        %name.appdata.xml
 # https://github.com/prusa3d/PrusaSlicer/pull/4340
 Patch1:         endian.patch
 
+# Include <atomic> for std::atomic where needed
+# Fixes build with Boost 1.75
+# https://github.com/prusa3d/PrusaSlicer/commit/44f71f0ed1
+Patch2:         atomic.patch
+
 # Highly-parallel uild can run out of memory on PPC64le
 %ifarch ppc64le
 %global _smp_ncpus_max 8