Use unordered_xxx classes detected by configure

When using configure, use the same family of hash sets/maps when
building wxWidgets and the applications using it as doing otherwise
results in ABI incompatibility.

include/wx/defs.h

@@ -377,6 +377,12 @@ typedef short int WXTYPE;
     #endif
 #endif
 
+/*
+    If using configure, stick to the options detected by it even if different
+    compiler options could result in detecting something different here, as it
+    would cause ABI issues otherwise (see #18034).
+*/
+#ifndef __WX_SETUP_H__
     /*
         Check for C++11 compilers, it is important to do it before the
         __has_include() checks because at least g++ 4.9.2+ __has_include() returns
@@ -412,6 +418,7 @@ typedef short int WXTYPE;
     #endif /* defined(__has_include) */
 
     #endif /* __cplusplus */
+#endif /* __WX_SETUP_H__ */
 
 /* provide replacement for C99 va_copy() if the compiler doesn't have it */