Fix T60434: crash with OSL and viewport + preview render at the same time.

Don't free LLVM JIT memory until process exit, there might be multiple OSL
instances using it.

intern/cycles/render/osl.cpp

@@ -66,6 +66,10 @@ OSLShaderManager::~OSLShaderManager()
 {
 	shading_system_free();
 	texture_system_free();
+}
+
+void OSLShaderManager::free_memory()
+{
 #ifdef OSL_HAS_BLENDER_CLEANUP_FIX
 	/* There is a problem with llvm+osl: The order global destructors across
 	 * different compilation units run cannot be guaranteed, on windows this means

intern/cycles/render/osl.h

@@ -70,6 +70,8 @@ public:
 	OSLShaderManager();
 	~OSLShaderManager();
 
+	static void free_memory();
+
 	void reset(Scene *scene);
 
 	bool use_osl() { return true; }

intern/cycles/render/shader.cpp

@@ -692,6 +692,10 @@ void ShaderManager::get_requested_features(Scene *scene,
 void ShaderManager::free_memory()
 {
 	beckmann_table.free_memory();
+
+#ifdef WITH_OSL
+	OSLShaderManager::free_memory();
+#endif
 }
 
 float ShaderManager::linear_rgb_to_gray(float3 c)