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This is caused by a change in GCC 10 defaults from -fcommon to -fno-common :
GCC now defaults to -fno-common. As a result, global variable accesses are more efficient on various targets. In C, global variables with multiple tentative definitions now result in linker errors. With -fcommon such definitions are silently merged during linking.
If compiled with -fcommon it builds OK. The better solution is to fix the code to define the variables just once.