GCC: Disable deprecated-enum-enum-conversion for gcc as well (#4997)

imgui_widgets.cpp

@@ -82,6 +82,7 @@ Index of this file:
 #pragma GCC diagnostic ignored "-Wpragmas"                          // warning: unknown option after '#pragma GCC diagnostic' kind
 #pragma GCC diagnostic ignored "-Wformat-nonliteral"                // warning: format not a string literal, format string not checked
 #pragma GCC diagnostic ignored "-Wclass-memaccess"                  // [__GNUC__ >= 8] warning: 'memset/memcpy' clearing/writing an object of type 'xxxx' with no trivial copy-assignment; use assignment or value-initialization instead
+#pragma GCC diagnostic ignored "-Wdeprecated-enum-enum-conversion"  // warning: bitwise operation between different enumeration types ('XXXFlags_' and 'XXXFlagsPrivate_') is deprecated
 #endif
 
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