Update GetFunctionPointerForDelegate docs (#3706)

Author: nxtn

xml/System.Runtime.InteropServices/Marshal.xml

@@ -3597,7 +3597,7 @@
           <format type="text/markdown"><![CDATA[  
 
 ## Remarks  
- The delegate `d` is converted to a function pointer that can be passed to unmanaged code using the [__stdcall](/cpp/cpp/stdcall) calling convention. You can set the calling convention by applying the <xref:System.Runtime.InteropServices.UnmanagedFunctionPointerAttribute> to the delegate.  
+ The delegate `d` is converted to a function pointer that can be passed to unmanaged code using the [__stdcall](/cpp/cpp/stdcall) calling convention on Windows, or the [__cdecl](/cpp/cpp/cdecl) calling convention on Linux and macOS. You can set the calling convention by applying the <xref:System.Runtime.InteropServices.UnmanagedFunctionPointerAttribute> to the delegate.  
 
  You must manually keep the delegate from being collected by the garbage collector from managed code. The garbage collector does not track references to unmanaged code.  
 
@@ -3661,7 +3661,7 @@
           <format type="text/markdown"><![CDATA[  
 
 ## Remarks  
- The delegate `d` is converted to a function pointer that can be passed to unmanaged code by using the [__stdcall](/cpp/cpp/stdcall) calling convention. You can set the calling convention by applying the <xref:System.Runtime.InteropServices.UnmanagedFunctionPointerAttribute> to the delegate.  
+ The delegate `d` is converted to a function pointer that can be passed to unmanaged code by using the [__stdcall](/cpp/cpp/stdcall) calling convention on Windows, or the [__cdecl](/cpp/cpp/cdecl) calling convention on Linux and macOS. You can set the calling convention by applying the <xref:System.Runtime.InteropServices.UnmanagedFunctionPointerAttribute> to the delegate.  
 
  You must manually keep the delegate from being collected by the garbage collector from managed code. The garbage collector does not track references to unmanaged code.