Linking errors when compiling with gcc 10

error.txt

The difference in this respect between gcc 10 and gcc 9 is that gcc 10 defaults to using -fno-common.

I am able to compile with gcc 10 by adding -fcommon to the CFLAGS, but this is not the proper way to fix it.

see https://gcc.gnu.org/gcc-10/porting_to.html