Fix compilation error with stricg GCC flags

intern/cycles/kernel/kernel_sse2.cpp

@@ -74,6 +74,7 @@ CCL_NAMESPACE_END
 #else
 
 /* needed for some linkers in combination with scons making empty compilation unit in a library */
-void __dummy_function_cycles_sse2(){}
+void __dummy_function_cycles_sse2(void);
+void __dummy_function_cycles_sse2(void){}
 
 #endif

intern/cycles/kernel/kernel_sse3.cpp

@@ -75,6 +75,7 @@ CCL_NAMESPACE_END
 #else
 
 /* needed for some linkers in combination with scons making empty compilation unit in a library */
-void __dummy_function_cycles_sse3(){}
+void __dummy_function_cycles_sse3(void);
+void __dummy_function_cycles_sse3(void){}
 
 #endif

intern/cycles/kernel/kernel_sse41.cpp

@@ -76,6 +76,7 @@ CCL_NAMESPACE_END
 #else
 
 /* needed for some linkers in combination with scons making empty compilation unit in a library */
-void __dummy_function_cycles_sse41(){}
+void __dummy_function_cycles_sse41(void);
+void __dummy_function_cycles_sse41(void){}
 
 #endif