Fix harmless unused parameters warnings in builds without wxLogTrace().

Fix warnings appearing when building with --disable-debug under Unix by
either referencing the parameters or variables which become unused then,
because wxLogTrace() calls are compiled out, or by not compiling the code
whose only purpose is to call wxLogTrace() at all.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@76786 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/unix/stackwalk.cpp

@@ -215,6 +215,8 @@ bool ReadLine(FILE* fp, unsigned long num, wxString* line)
 {
     if ( !fgets(g_buf, WXSIZEOF(g_buf), fp) )
     {
+        wxUnusedVar(num); // could be unused if debug tracing is disabled
+
         wxLogDebug(wxS("cannot read address information for stack frame #%lu"),
                    num);
         return false;