Fixed weak def of __cxa_pure_virtual()

flips.cpp

@@ -11,7 +11,10 @@
 void* operator new(size_t n) { return malloc(n); } // forget allocation failures, let them segfault.
 void operator delete(void * p) { free(p); }
 void operator delete(void * p, size_t n) { free(p); }
-extern "C" void __cxa_pure_virtual() { abort(); }
+// removed extern
+//     https://github.com/Alcaro/Flips/issues/26#issuecomment-573674247
+//     https://github.com/Alcaro/Flips/issues/32#issuecomment-1036141144
+//extern "C" void __cxa_pure_virtual() { abort(); }
 
 #if __GNUC__ && (__cpp_rtti || __cpp_exceptions)
 #warning "Consider building with -fno-exceptions -fno-rtti, to avoid dependencies on libgcc_s_sjlj-1.dll and libstdc++-6.dll."