Update error-memcpy-param-overlap.md

Author: branh

docs/sanitizers/error-memcpy-param-overlap.md

@@ -35,10 +35,12 @@ int main(int argc, char **argv) {
 To build and test this example, run these commands in a Visual Studio 2019 version 16.9 or later [developer command prompt](../build/building-on-the-command-line.md#developer_command_prompt_shortcuts):
 
 ```cmd
-cl example1.cpp /fsanitize=address /Zi
+cl example1.cpp /fsanitize=address /Zi /Oi
 devenv /debugexe example1.exe
 ```
 
+The [/Oi flag](../../build/reference/oi-generate-intrinsic-functions) tells the compiler to treat memcpy and memmove as intrinsic functions. This is necessary because some versions of the standard library implement memcpy and memmove in the same way and ASAN only detects bad code that is actually executed.
+
 ### Resulting error
 
 :::image type="content" source="media/memcpy-param-overlap-example-1.png" alt-text="Screenshot of debugger displaying memcpy-param-overlap error in example 1.":::