Address #313: try to guard against strict-aliasing bugs with gsl::byte

* Add test to demonstrate byte aliasing problem on g++ and clang++

* Add note about no-strict-aliasing flag in README

* Activate aliasing unit test and use -fno-strict-aliasing flag

tests/byte_tests.cpp

@@ -43,7 +43,7 @@ SUITE(byte_tests)
             byte b = byte(12);
             CHECK(static_cast<unsigned char>(b) == 12);
         }
-        
+
         {
             byte b = to_byte<12>();
             CHECK(static_cast<unsigned char>(b) == 12);
@@ -114,6 +114,20 @@ SUITE(byte_tests)
 //      CHECK(0x12 == gsl::to_integer<float>(b));   // expect compile-time error
 //      CHECK(0x12 == gsl::to_integer<double>(b));  // expect compile-time error
     }
+
+    int modify_both(gsl::byte& b, int& i)
+    {
+        i = 10;
+        b = to_byte<5>();
+        return i;
+    }
+
+    TEST(aliasing)
+    {
+        int i{ 0 };
+        int res = modify_both(reinterpret_cast<byte&>(i), i);
+        CHECK(res == i);
+    }
 }
 
 }