Fixed minor zealous Clang warning (demo code intentionally uses strdup() to be copiable)

imgui.cpp

@@ -453,6 +453,7 @@
 #pragma clang diagnostic ignored "-Wglobal-constructors"    // warning : declaration requires a global destructor           // similar to above, not sure what the exact difference it.
 #pragma clang diagnostic ignored "-Wsign-conversion"        // warning : implicit conversion changes signedness             // 
 #pragma clang diagnostic ignored "-Wmissing-noreturn"       // warning : function xx could be declared with attribute 'noreturn' warning    // GetDefaultFontData() asserts which some implementation makes it never return.
+#pragma clang diagnostic ignored "-Wdeprecated-declarations"// warning : 'xx' is deprecated: The POSIX name for this item.. // for strdup used in demo code (so user can copy & paste the code)
 #endif
 #ifdef __GNUC__
 #pragma GCC diagnostic ignored "-Wunused-function"          // warning: 'xxxx' defined but not used