Fixed compiler warnings

g++-10.1.0/c++20:

'error: compound assignment with ‘volatile’-qualified left operand is deprecated [-Werror=volatile]'

glm/detail/type_half.inl

@@ -6,7 +6,7 @@ namespace detail
 		volatile float f = 1e10;
 
 		for(int i = 0; i < 10; ++i)
-			f *= f; // this will overflow before the for loop terminates
+			f = f * f; // this will overflow before the for loop terminates
 		return f;
 	}